Re: [PATCH v5 4/6] tools/mount-flatpak: init

[Demi Marie Obenour <demiobenour@gmail.com>]

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On 12/1/25 14:00, Demi Marie Obenour wrote:
> On 12/1/25 12:04, Alyssa Ross wrote:
>> I tried to build this with Meson, but pathrs depends on thiserror,
>> which tries to read OUT_DIR, and support for setting that isn't
>> currently in a Meson release, and requires nightly Rust, so build with
>> Cargo for now and we can revisit that later.
>>
>> Link: https://github.com/mesonbuild/meson/pull/15148
>> Link: https://github.com/rust-lang/rust/issues/118372
>> Signed-off-by: Alyssa Ross <hi@alyssa.is>
>> ---
>> v5: • Extract mount_commit() function
>>     • Expand safety comment.
>> v4: https://spectrum-os.org/lists/archives/spectrum-devel/20251201044534.977524-5-hi@alyssa.is/
>>
>>  LICENSES/MPL-2.0.txt                   | 373 +++++++++++++++++++++++++
>>  pkgs/default.nix                       |   1 +
>>  tools/mount-flatpak/Cargo.lock         | 238 ++++++++++++++++
>>  tools/mount-flatpak/Cargo.lock.license |   2 +
>>  tools/mount-flatpak/Cargo.toml         |  11 +
>>  tools/mount-flatpak/config             |   7 +
>>  tools/mount-flatpak/default.nix        |  25 ++
>>  tools/mount-flatpak/src/keyfile.rs     | 189 +++++++++++++
>>  tools/mount-flatpak/src/main.rs        | 288 +++++++++++++++++++
>>  tools/mount-flatpak/src/metadata.rs    |  19 ++
>>  10 files changed, 1153 insertions(+)
>>  create mode 100644 LICENSES/MPL-2.0.txt
>>  create mode 100644 tools/mount-flatpak/Cargo.lock
>>  create mode 100644 tools/mount-flatpak/Cargo.lock.license
>>  create mode 100644 tools/mount-flatpak/Cargo.toml
>>  create mode 100644 tools/mount-flatpak/config
>>  create mode 100644 tools/mount-flatpak/default.nix
>>  create mode 100644 tools/mount-flatpak/src/keyfile.rs
>>  create mode 100644 tools/mount-flatpak/src/main.rs
>>  create mode 100644 tools/mount-flatpak/src/metadata.rs
>>
>> diff --git a/LICENSES/MPL-2.0.txt b/LICENSES/MPL-2.0.txt
>> new file mode 100644
>> index 0000000..d0a1fa1
>> --- /dev/null
>> +++ b/LICENSES/MPL-2.0.txt
>> @@ -0,0 +1,373 @@
>> +Mozilla Public License Version 2.0
>> +==================================
>> +
>> +1. Definitions
>> +--------------
>> +
>> +1.1. "Contributor"
>> +    means each individual or legal entity that creates, contributes to
>> +    the creation of, or owns Covered Software.
>> +
>> +1.2. "Contributor Version"
>> +    means the combination of the Contributions of others (if any) used
>> +    by a Contributor and that particular Contributor's Contribution.
>> +
>> +1.3. "Contribution"
>> +    means Covered Software of a particular Contributor.
>> +
>> +1.4. "Covered Software"
>> +    means Source Code Form to which the initial Contributor has attached
>> +    the notice in Exhibit A, the Executable Form of such Source Code
>> +    Form, and Modifications of such Source Code Form, in each case
>> +    including portions thereof.
>> +
>> +1.5. "Incompatible With Secondary Licenses"
>> +    means
>> +
>> +    (a) that the initial Contributor has attached the notice described
>> +        in Exhibit B to the Covered Software; or
>> +
>> +    (b) that the Covered Software was made available under the terms of
>> +        version 1.1 or earlier of the License, but not also under the
>> +        terms of a Secondary License.
>> +
>> +1.6. "Executable Form"
>> +    means any form of the work other than Source Code Form.
>> +
>> +1.7. "Larger Work"
>> +    means a work that combines Covered Software with other material, in
>> +    a separate file or files, that is not Covered Software.
>> +
>> +1.8. "License"
>> +    means this document.
>> +
>> +1.9. "Licensable"
>> +    means having the right to grant, to the maximum extent possible,
>> +    whether at the time of the initial grant or subsequently, any and
>> +    all of the rights conveyed by this License.
>> +
>> +1.10. "Modifications"
>> +    means any of the following:
>> +
>> +    (a) any file in Source Code Form that results from an addition to,
>> +        deletion from, or modification of the contents of Covered
>> +        Software; or
>> +
>> +    (b) any new file in Source Code Form that contains any Covered
>> +        Software.
>> +
>> +1.11. "Patent Claims" of a Contributor
>> +    means any patent claim(s), including without limitation, method,
>> +    process, and apparatus claims, in any patent Licensable by such
>> +    Contributor that would be infringed, but for the grant of the
>> +    License, by the making, using, selling, offering for sale, having
>> +    made, import, or transfer of either its Contributions or its
>> +    Contributor Version.
>> +
>> +1.12. "Secondary License"
>> +    means either the GNU General Public License, Version 2.0, the GNU
>> +    Lesser General Public License, Version 2.1, the GNU Affero General
>> +    Public License, Version 3.0, or any later versions of those
>> +    licenses.
>> +
>> +1.13. "Source Code Form"
>> +    means the form of the work preferred for making modifications.
>> +
>> +1.14. "You" (or "Your")
>> +    means an individual or a legal entity exercising rights under this
>> +    License. For legal entities, "You" includes any entity that
>> +    controls, is controlled by, or is under common control with You. For
>> +    purposes of this definition, "control" means (a) the power, direct
>> +    or indirect, to cause the direction or management of such entity,
>> +    whether by contract or otherwise, or (b) ownership of more than
>> +    fifty percent (50%) of the outstanding shares or beneficial
>> +    ownership of such entity.
>> +
>> +2. License Grants and Conditions
>> +--------------------------------
>> +
>> +2.1. Grants
>> +
>> +Each Contributor hereby grants You a world-wide, royalty-free,
>> +non-exclusive license:
>> +
>> +(a) under intellectual property rights (other than patent or trademark)
>> +    Licensable by such Contributor to use, reproduce, make available,
>> +    modify, display, perform, distribute, and otherwise exploit its
>> +    Contributions, either on an unmodified basis, with Modifications, or
>> +    as part of a Larger Work; and
>> +
>> +(b) under Patent Claims of such Contributor to make, use, sell, offer
>> +    for sale, have made, import, and otherwise transfer either its
>> +    Contributions or its Contributor Version.
>> +
>> +2.2. Effective Date
>> +
>> +The licenses granted in Section 2.1 with respect to any Contribution
>> +become effective for each Contribution on the date the Contributor first
>> +distributes such Contribution.
>> +
>> +2.3. Limitations on Grant Scope
>> +
>> +The licenses granted in this Section 2 are the only rights granted under
>> +this License. No additional rights or licenses will be implied from the
>> +distribution or licensing of Covered Software under this License.
>> +Notwithstanding Section 2.1(b) above, no patent license is granted by a
>> +Contributor:
>> +
>> +(a) for any code that a Contributor has removed from Covered Software;
>> +    or
>> +
>> +(b) for infringements caused by: (i) Your and any other third party's
>> +    modifications of Covered Software, or (ii) the combination of its
>> +    Contributions with other software (except as part of its Contributor
>> +    Version); or
>> +
>> +(c) under Patent Claims infringed by Covered Software in the absence of
>> +    its Contributions.
>> +
>> +This License does not grant any rights in the trademarks, service marks,
>> +or logos of any Contributor (except as may be necessary to comply with
>> +the notice requirements in Section 3.4).
>> +
>> +2.4. Subsequent Licenses
>> +
>> +No Contributor makes additional grants as a result of Your choice to
>> +distribute the Covered Software under a subsequent version of this
>> +License (see Section 10.2) or under the terms of a Secondary License (if
>> +permitted under the terms of Section 3.3).
>> +
>> +2.5. Representation
>> +
>> +Each Contributor represents that the Contributor believes its
>> +Contributions are its original creation(s) or it has sufficient rights
>> +to grant the rights to its Contributions conveyed by this License.
>> +
>> +2.6. Fair Use
>> +
>> +This License is not intended to limit any rights You have under
>> +applicable copyright doctrines of fair use, fair dealing, or other
>> +equivalents.
>> +
>> +2.7. Conditions
>> +
>> +Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted
>> +in Section 2.1.
>> +
>> +3. Responsibilities
>> +-------------------
>> +
>> +3.1. Distribution of Source Form
>> +
>> +All distribution of Covered Software in Source Code Form, including any
>> +Modifications that You create or to which You contribute, must be under
>> +the terms of this License. You must inform recipients that the Source
>> +Code Form of the Covered Software is governed by the terms of this
>> +License, and how they can obtain a copy of this License. You may not
>> +attempt to alter or restrict the recipients' rights in the Source Code
>> +Form.
>> +
>> +3.2. Distribution of Executable Form
>> +
>> +If You distribute Covered Software in Executable Form then:
>> +
>> +(a) such Covered Software must also be made available in Source Code
>> +    Form, as described in Section 3.1, and You must inform recipients of
>> +    the Executable Form how they can obtain a copy of such Source Code
>> +    Form by reasonable means in a timely manner, at a charge no more
>> +    than the cost of distribution to the recipient; and
>> +
>> +(b) You may distribute such Executable Form under the terms of this
>> +    License, or sublicense it under different terms, provided that the
>> +    license for the Executable Form does not attempt to limit or alter
>> +    the recipients' rights in the Source Code Form under this License.
>> +
>> +3.3. Distribution of a Larger Work
>> +
>> +You may create and distribute a Larger Work under terms of Your choice,
>> +provided that You also comply with the requirements of this License for
>> +the Covered Software. If the Larger Work is a combination of Covered
>> +Software with a work governed by one or more Secondary Licenses, and the
>> +Covered Software is not Incompatible With Secondary Licenses, this
>> +License permits You to additionally distribute such Covered Software
>> +under the terms of such Secondary License(s), so that the recipient of
>> +the Larger Work may, at their option, further distribute the Covered
>> +Software under the terms of either this License or such Secondary
>> +License(s).
>> +
>> +3.4. Notices
>> +
>> +You may not remove or alter the substance of any license notices
>> +(including copyright notices, patent notices, disclaimers of warranty,
>> +or limitations of liability) contained within the Source Code Form of
>> +the Covered Software, except that You may alter any license notices to
>> +the extent required to remedy known factual inaccuracies.
>> +
>> +3.5. Application of Additional Terms
>> +
>> +You may choose to offer, and to charge a fee for, warranty, support,
>> +indemnity or liability obligations to one or more recipients of Covered
>> +Software. However, You may do so only on Your own behalf, and not on
>> +behalf of any Contributor. You must make it absolutely clear that any
>> +such warranty, support, indemnity, or liability obligation is offered by
>> +You alone, and You hereby agree to indemnify every Contributor for any
>> +liability incurred by such Contributor as a result of warranty, support,
>> +indemnity or liability terms You offer. You may include additional
>> +disclaimers of warranty and limitations of liability specific to any
>> +jurisdiction.
>> +
>> +4. Inability to Comply Due to Statute or Regulation
>> +---------------------------------------------------
>> +
>> +If it is impossible for You to comply with any of the terms of this
>> +License with respect to some or all of the Covered Software due to
>> +statute, judicial order, or regulation then You must: (a) comply with
>> +the terms of this License to the maximum extent possible; and (b)
>> +describe the limitations and the code they affect. Such description must
>> +be placed in a text file included with all distributions of the Covered
>> +Software under this License. Except to the extent prohibited by statute
>> +or regulation, such description must be sufficiently detailed for a
>> +recipient of ordinary skill to be able to understand it.
>> +
>> +5. Termination
>> +--------------
>> +
>> +5.1. The rights granted under this License will terminate automatically
>> +if You fail to comply with any of its terms. However, if You become
>> +compliant, then the rights granted under this License from a particular
>> +Contributor are reinstated (a) provisionally, unless and until such
>> +Contributor explicitly and finally terminates Your grants, and (b) on an
>> +ongoing basis, if such Contributor fails to notify You of the
>> +non-compliance by some reasonable means prior to 60 days after You have
>> +come back into compliance. Moreover, Your grants from a particular
>> +Contributor are reinstated on an ongoing basis if such Contributor
>> +notifies You of the non-compliance by some reasonable means, this is the
>> +first time You have received notice of non-compliance with this License
>> +from such Contributor, and You become compliant prior to 30 days after
>> +Your receipt of the notice.
>> +
>> +5.2. If You initiate litigation against any entity by asserting a patent
>> +infringement claim (excluding declaratory judgment actions,
>> +counter-claims, and cross-claims) alleging that a Contributor Version
>> +directly or indirectly infringes any patent, then the rights granted to
>> +You by any and all Contributors for the Covered Software under Section
>> +2.1 of this License shall terminate.
>> +
>> +5.3. In the event of termination under Sections 5.1 or 5.2 above, all
>> +end user license agreements (excluding distributors and resellers) which
>> +have been validly granted by You or Your distributors under this License
>> +prior to termination shall survive termination.
>> +
>> +************************************************************************
>> +*                                                                      *
>> +*  6. Disclaimer of Warranty                                           *
>> +*  -------------------------                                           *
>> +*                                                                      *
>> +*  Covered Software is provided under this License on an "as is"       *
>> +*  basis, without warranty of any kind, either expressed, implied, or  *
>> +*  statutory, including, without limitation, warranties that the       *
>> +*  Covered Software is free of defects, merchantable, fit for a        *
>> +*  particular purpose or non-infringing. The entire risk as to the     *
>> +*  quality and performance of the Covered Software is with You.        *
>> +*  Should any Covered Software prove defective in any respect, You     *
>> +*  (not any Contributor) assume the cost of any necessary servicing,   *
>> +*  repair, or correction. This disclaimer of warranty constitutes an   *
>> +*  essential part of this License. No use of any Covered Software is   *
>> +*  authorized under this License except under this disclaimer.         *
>> +*                                                                      *
>> +************************************************************************
>> +
>> +************************************************************************
>> +*                                                                      *
>> +*  7. Limitation of Liability                                          *
>> +*  --------------------------                                          *
>> +*                                                                      *
>> +*  Under no circumstances and under no legal theory, whether tort      *
>> +*  (including negligence), contract, or otherwise, shall any           *
>> +*  Contributor, or anyone who distributes Covered Software as          *
>> +*  permitted above, be liable to You for any direct, indirect,         *
>> +*  special, incidental, or consequential damages of any character      *
>> +*  including, without limitation, damages for lost profits, loss of    *
>> +*  goodwill, work stoppage, computer failure or malfunction, or any    *
>> +*  and all other commercial damages or losses, even if such party      *
>> +*  shall have been informed of the possibility of such damages. This   *
>> +*  limitation of liability shall not apply to liability for death or   *
>> +*  personal injury resulting from such party's negligence to the       *
>> +*  extent applicable law prohibits such limitation. Some               *
>> +*  jurisdictions do not allow the exclusion or limitation of           *
>> +*  incidental or consequential damages, so this exclusion and          *
>> +*  limitation may not apply to You.                                    *
>> +*                                                                      *
>> +************************************************************************
>> +
>> +8. Litigation
>> +-------------
>> +
>> +Any litigation relating to this License may be brought only in the
>> +courts of a jurisdiction where the defendant maintains its principal
>> +place of business and such litigation shall be governed by laws of that
>> +jurisdiction, without reference to its conflict-of-law provisions.
>> +Nothing in this Section shall prevent a party's ability to bring
>> +cross-claims or counter-claims.
>> +
>> +9. Miscellaneous
>> +----------------
>> +
>> +This License represents the complete agreement concerning the subject
>> +matter hereof. If any provision of this License is held to be
>> +unenforceable, such provision shall be reformed only to the extent
>> +necessary to make it enforceable. Any law or regulation which provides
>> +that the language of a contract shall be construed against the drafter
>> +shall not be used to construe this License against a Contributor.
>> +
>> +10. Versions of the License
>> +---------------------------
>> +
>> +10.1. New Versions
>> +
>> +Mozilla Foundation is the license steward. Except as provided in Section
>> +10.3, no one other than the license steward has the right to modify or
>> +publish new versions of this License. Each version will be given a
>> +distinguishing version number.
>> +
>> +10.2. Effect of New Versions
>> +
>> +You may distribute the Covered Software under the terms of the version
>> +of the License under which You originally received the Covered Software,
>> +or under the terms of any subsequent version published by the license
>> +steward.
>> +
>> +10.3. Modified Versions
>> +
>> +If you create software not governed by this License, and you want to
>> +create a new license for such software, you may create and use a
>> +modified version of this License if you rename the license and remove
>> +any references to the name of the license steward (except to note that
>> +such modified license differs from this License).
>> +
>> +10.4. Distributing Source Code Form that is Incompatible With Secondary
>> +Licenses
>> +
>> +If You choose to distribute Source Code Form that is Incompatible With
>> +Secondary Licenses under the terms of this version of the License, the
>> +notice described in Exhibit B of this License must be attached.
>> +
>> +Exhibit A - Source Code Form License Notice
>> +-------------------------------------------
>> +
>> +  This Source Code Form is subject to the terms of the Mozilla Public
>> +  License, v. 2.0. If a copy of the MPL was not distributed with this
>> +  file, You can obtain one at https://mozilla.org/MPL/2.0/.
>> +
>> +If it is not possible or desirable to put the notice in a particular
>> +file, then You may include the notice in a location (such as a LICENSE
>> +file in a relevant directory) where a recipient would be likely to look
>> +for such a notice.
>> +
>> +You may add additional accurate notices of copyright ownership.
>> +
>> +Exhibit B - "Incompatible With Secondary Licenses" Notice
>> +---------------------------------------------------------
>> +
>> +  This Source Code Form is "Incompatible With Secondary Licenses", as
>> +  defined by the Mozilla Public License, v. 2.0.
>> diff --git a/pkgs/default.nix b/pkgs/default.nix
>> index bc25420..29fefb4 100644
>> --- a/pkgs/default.nix
>> +++ b/pkgs/default.nix
>> @@ -36,6 +36,7 @@ let
>>        path: (import path { inherit (self) callPackage; }).override;
>>  
>>      rootfs = self.callSpectrumPackage ../host/rootfs {};
>> +    mount-flatpak = self.callSpectrumPackage ../tools/mount-flatpak {};
>>      spectrum-build-tools = self.callSpectrumPackage ../tools {
>>        appSupport = false;
>>        buildSupport = true;
>> diff --git a/tools/mount-flatpak/Cargo.lock b/tools/mount-flatpak/Cargo.lock
>> new file mode 100644
>> index 0000000..8cb5663
>> --- /dev/null
>> +++ b/tools/mount-flatpak/Cargo.lock
>> @@ -0,0 +1,238 @@
>> +# This file is automatically @generated by Cargo.
>> +# It is not intended for manual editing.
>> +version = 4
>> +
>> +[[package]]
>> +name = "bitflags"
>> +version = "2.10.0"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "812e12b5285cc515a9c72a5c1d3b6d46a19dac5acfef5265968c166106e31dd3"
>> +
>> +[[package]]
>> +name = "cfg-if"
>> +version = "1.0.4"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
>> +
>> +[[package]]
>> +name = "either"
>> +version = "1.15.0"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
>> +
>> +[[package]]
>> +name = "errno"
>> +version = "0.3.14"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
>> +dependencies = [
>> + "libc",
>> + "windows-sys",
>> +]
>> +
>> +[[package]]
>> +name = "fastrand"
>> +version = "2.3.0"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "37909eebbb50d72f9059c3b6d82c0463f2ff062c9e95845c43a6c9c0355411be"
>> +
>> +[[package]]
>> +name = "getrandom"
>> +version = "0.3.4"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "899def5c37c4fd7b2664648c28120ecec138e4d395b459e5ca34f9cce2dd77fd"
>> +dependencies = [
>> + "cfg-if",
>> + "libc",
>> + "r-efi",
>> + "wasip2",
>> +]
>> +
>> +[[package]]
>> +name = "itertools"
>> +version = "0.14.0"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "2b192c782037fadd9cfa75548310488aabdbf3d2da73885b31bd0abd03351285"
>> +dependencies = [
>> + "either",
>> +]
>> +
>> +[[package]]
>> +name = "libc"
>> +version = "0.2.177"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "2874a2af47a2325c2001a6e6fad9b16a53b802102b528163885171cf92b15976"
>> +
>> +[[package]]
>> +name = "linux-raw-sys"
>> +version = "0.11.0"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "df1d3c3b53da64cf5760482273a98e575c651a67eec7f77df96b5b642de8f039"
>> +
>> +[[package]]
>> +name = "memchr"
>> +version = "2.7.6"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "f52b00d39961fc5b2736ea853c9cc86238e165017a493d1d5c8eac6bdc4cc273"
>> +
>> +[[package]]
>> +name = "mount-flatpak"
>> +version = "0.0.0"
>> +dependencies = [
>> + "libc",
>> + "pathrs",
>> + "rustix",
>> +]
>> +
>> +[[package]]
>> +name = "once_cell"
>> +version = "1.21.3"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "42f5e15c9953c5e4ccceeb2e7382a716482c34515315f7b03532b8b4e8393d2d"
>> +
>> +[[package]]
>> +name = "pathrs"
>> +version = "0.2.1"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "c63f58f2463b3eecc7d285eace144d8c4820631d018d927049f8569be4b3b1a4"
>> +dependencies = [
>> + "bitflags",
>> + "itertools",
>> + "libc",
>> + "memchr",
>> + "once_cell",
>> + "rustix",
>> + "rustversion",
>> + "static_assertions",
>> + "tempfile",
>> + "thiserror",
>> +]
>> +
>> +[[package]]
>> +name = "proc-macro2"
>> +version = "1.0.103"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "5ee95bc4ef87b8d5ba32e8b7714ccc834865276eab0aed5c9958d00ec45f49e8"
>> +dependencies = [
>> + "unicode-ident",
>> +]
>> +
>> +[[package]]
>> +name = "quote"
>> +version = "1.0.42"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "a338cc41d27e6cc6dce6cefc13a0729dfbb81c262b1f519331575dd80ef3067f"
>> +dependencies = [
>> + "proc-macro2",
>> +]
>> +
>> +[[package]]
>> +name = "r-efi"
>> +version = "5.3.0"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "69cdb34c158ceb288df11e18b4bd39de994f6657d83847bdffdbd7f346754b0f"
>> +
>> +[[package]]
>> +name = "rustix"
>> +version = "1.1.2"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "cd15f8a2c5551a84d56efdc1cd049089e409ac19a3072d5037a17fd70719ff3e"
>> +dependencies = [
>> + "bitflags",
>> + "errno",
>> + "libc",
>> + "linux-raw-sys",
>> + "windows-sys",
>> +]
>> +
>> +[[package]]
>> +name = "rustversion"
>> +version = "1.0.22"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
>> +
>> +[[package]]
>> +name = "static_assertions"
>> +version = "1.1.0"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
>> +
>> +[[package]]
>> +name = "syn"
>> +version = "2.0.111"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "390cc9a294ab71bdb1aa2e99d13be9c753cd2d7bd6560c77118597410c4d2e87"
>> +dependencies = [
>> + "proc-macro2",
>> + "quote",
>> + "unicode-ident",
>> +]
>> +
>> +[[package]]
>> +name = "tempfile"
>> +version = "3.23.0"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "2d31c77bdf42a745371d260a26ca7163f1e0924b64afa0b688e61b5a9fa02f16"
>> +dependencies = [
>> + "fastrand",
>> + "getrandom",
>> + "once_cell",
>> + "rustix",
>> + "windows-sys",
>> +]
>> +
>> +[[package]]
>> +name = "thiserror"
>> +version = "2.0.17"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "f63587ca0f12b72a0600bcba1d40081f830876000bb46dd2337a3051618f4fc8"
>> +dependencies = [
>> + "thiserror-impl",
>> +]
>> +
>> +[[package]]
>> +name = "thiserror-impl"
>> +version = "2.0.17"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "3ff15c8ecd7de3849db632e14d18d2571fa09dfc5ed93479bc4485c7a517c913"
>> +dependencies = [
>> + "proc-macro2",
>> + "quote",
>> + "syn",
>> +]
>> +
>> +[[package]]
>> +name = "unicode-ident"
>> +version = "1.0.22"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "9312f7c4f6ff9069b165498234ce8be658059c6728633667c526e27dc2cf1df5"
>> +
>> +[[package]]
>> +name = "wasip2"
>> +version = "1.0.1+wasi-0.2.4"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "0562428422c63773dad2c345a1882263bbf4d65cf3f42e90921f787ef5ad58e7"
>> +dependencies = [
>> + "wit-bindgen",
>> +]
>> +
>> +[[package]]
>> +name = "windows-link"
>> +version = "0.2.1"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
>> +
>> +[[package]]
>> +name = "windows-sys"
>> +version = "0.61.2"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
>> +dependencies = [
>> + "windows-link",
>> +]
>> +
>> +[[package]]
>> +name = "wit-bindgen"
>> +version = "0.46.0"
>> +source = "registry+https://github.com/rust-lang/crates.io-index"
>> +checksum = "f17a85883d4e6d00e8a97c586de764dabcc06133f7f1d55dce5cdc070ad7fe59"
>> diff --git a/tools/mount-flatpak/Cargo.lock.license b/tools/mount-flatpak/Cargo.lock.license
>> new file mode 100644
>> index 0000000..d705e97
>> --- /dev/null
>> +++ b/tools/mount-flatpak/Cargo.lock.license
>> @@ -0,0 +1,2 @@
>> +SPDX-License-Identifier: CC0-1.0
>> +SPDX-FileCopyrightText: 2024 Alyssa Ross <hi@alyssa.is>
>> diff --git a/tools/mount-flatpak/Cargo.toml b/tools/mount-flatpak/Cargo.toml
>> new file mode 100644
>> index 0000000..670be2f
>> --- /dev/null
>> +++ b/tools/mount-flatpak/Cargo.toml
>> @@ -0,0 +1,11 @@
>> +# SPDX-License-Identifier: CC0-1.0
>> +# SPDX-FileCopyrightText: 2025 Alyssa Ross <hi@alyssa.is>
>> +
>> +[package]
>> +name = "mount-flatpak"
>> +edition = "2024"
>> +
>> +[dependencies]
>> +libc = "0.2.177"
>> +pathrs = "0.2.1"
>> +rustix = "1.1.2"
>> diff --git a/tools/mount-flatpak/config b/tools/mount-flatpak/config
>> new file mode 100644
>> index 0000000..b3c2bee
>> --- /dev/null
>> +++ b/tools/mount-flatpak/config
>> @@ -0,0 +1,7 @@
>> +# SPDX-License-Identifier: CC0-1.0
>> +# SPDX-FileCopyrightText: 2025 Alyssa Ross <hi@alyssa.is>
>> +
>> +[core]
>> +repo_version=1
>> +mode=bare-user-only
>> +min-free-space-size=500MB
>> diff --git a/tools/mount-flatpak/default.nix b/tools/mount-flatpak/default.nix
>> new file mode 100644
>> index 0000000..f364fd7
>> --- /dev/null
>> +++ b/tools/mount-flatpak/default.nix
>> @@ -0,0 +1,25 @@
>> +# SPDX-FileCopyrightText: 2024-2025 Alyssa Ross <hi@alyssa.is>
>> +# SPDX-License-Identifier: MIT
>> +
>> +import ../../lib/call-package.nix (
>> +{ src, lib, rustPlatform }:
>> +
>> +rustPlatform.buildRustPackage {
>> +  name = "mount-flatpak";
>> +
>> +  src = lib.fileset.toSource {
>> +    root = ../..;
>> +    fileset = lib.fileset.intersection src ./.;
>> +  };
>> +  sourceRoot = "source/tools/mount-flatpak";
>> +
>> +  cargoLock.lockFile = ./Cargo.lock;
>> +
>> +  env = {
>> +    MOUNT_FLATPAK_CONFIG_PATH = "${placeholder "out"}/share/spectrum/flatpak-config";
>> +  };
>> +
>> +  postInstall = ''
>> +    install -Dm 0755 config $MOUNT_FLATPAK_CONFIG_PATH
>> +  '';
>> +}) (_: {})
>> diff --git a/tools/mount-flatpak/src/keyfile.rs b/tools/mount-flatpak/src/keyfile.rs
>> new file mode 100644
>> index 0000000..fa746b3
>> --- /dev/null
>> +++ b/tools/mount-flatpak/src/keyfile.rs
>> @@ -0,0 +1,189 @@
>> +// Copyright 2021 System76 <info@system76.com>
>> +// SPDX-FileCopyrightText: 2025 Alyssa Ross <hi@alyssa.is>
>> +// SPDX-License-Identifier: MPL-2.0
>> +
>> +// Adapted from freedesktop-desktop-entry 0.7.19.
>> +
>> +use std::collections::BTreeMap;
>> +use std::fmt::{self, Display, Formatter};
>> +
>> +type Group = BTreeMap<String, String>;
>> +
>> +#[derive(Debug)]
>> +pub enum DecodeError {
>> +    KeyValueWithoutAGroup,
>> +    InvalidKey,
>> +    InvalidValue,
>> +}
>> +
>> +impl Display for DecodeError {
>> +    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
>> +        match self {
>> +            Self::KeyValueWithoutAGroup => write!(f, "key/value without a group"),
>> +            Self::InvalidKey => write!(f, "invalid key"),
>> +            Self::InvalidValue => write!(f, "invalid value"),
>> +        }
>> +    }
>> +}
>> +
>> +pub fn parse(input: &str) -> Result<BTreeMap<String, Group>, DecodeError> {
>> +    let mut groups = BTreeMap::default();
>> +    let mut active_group: Option<ActiveGroup> = None;
>> +    let mut active_keys: Option<ActiveKeys> = None;
>> +
>> +    for line in input.lines() {
>> +        process_line(line, &mut groups, &mut active_group, &mut active_keys)?;
>> +    }
>> +
>> +    if let Some(active_keys) = active_keys.take() {
>> +        match &mut active_group {
>> +            Some(active_group) => {
>> +                active_group
>> +                    .group
>> +                    .insert(active_keys.key_name, active_keys.value);
>> +            }
>> +            None => return Err(DecodeError::KeyValueWithoutAGroup),
>> +        }
>> +    }
>> +
>> +    if let Some(mut group) = active_group.take() {
>> +        groups
>> +            .entry(group.group_name)
>> +            .or_default()
>> +            .append(&mut group.group);
>> +    }
>> +
>> +    Ok(groups)
>> +}
>> +
>> +struct ActiveGroup {
>> +    group_name: String,
>> +    group: Group,
>> +}
>> +
>> +struct ActiveKeys {
>> +    key_name: String,
>> +    value: String,
>> +}
>> +
>> +#[inline(never)]
>> +fn process_line(
>> +    line: &str,
>> +    groups: &mut BTreeMap<String, Group>,
>> +    active_group: &mut Option<ActiveGroup>,
>> +    active_keys: &mut Option<ActiveKeys>,
>> +) -> Result<(), DecodeError> {
>> +    if line.trim().is_empty() || line.starts_with('#') {
>> +        return Ok(());
>> +    }
>> +
>> +    let line_bytes = line.as_bytes();
>> +
>> +    // if group
>> +    if line_bytes[0] == b'[' {
>> +        if let Some(end) = line_bytes[1..].iter().rposition(|&b| b == b']') {
>> +            let group_name = &line[1..end + 1];
>> +
>> +            if let Some(active_keys) = active_keys.take() {
>> +                match active_group {
>> +                    Some(active_group) => {
>> +                        active_group
>> +                            .group
>> +                            .insert(active_keys.key_name, active_keys.value);
>> +                    }
>> +                    None => return Err(DecodeError::KeyValueWithoutAGroup),
>> +                }
>> +            }
>> +
>> +            if let Some(mut group) = active_group.take() {
>> +                groups
>> +                    .entry(group.group_name)
>> +                    .or_default()
>> +                    .append(&mut group.group);
>> +            }
>> +
>> +            active_group.replace(ActiveGroup {
>> +                group_name: group_name.to_string(),
>> +                group: Group::default(),
>> +            });
>> +        }
>> +    }
>> +    // else, if value
>> +    else if let Some(delimiter) = line_bytes.iter().position(|&b| b == b'=') {
>> +        let key = &line[..delimiter];
>> +        let value = format_value(&line[delimiter + 1..])?;
>> +
>> +        if key.is_empty() {
>> +            return Err(DecodeError::InvalidKey);
>> +        }
>> +
>> +        if let Some(active_keys) = active_keys.take() {
>> +            match active_group {
>> +                Some(active_group) => {
>> +                    active_group
>> +                        .group
>> +                        .insert(active_keys.key_name, active_keys.value);
>> +                }
>> +                None => return Err(DecodeError::KeyValueWithoutAGroup),
>> +            }
>> +        }
>> +        active_keys.replace(ActiveKeys {
>> +            key_name: key.trim().to_string(),
>> +            value,
>> +        });
>> +    }
>> +    Ok(())
>> +}
>> +
>> +// https://specifications.freedesktop.org/desktop-entry-spec/latest/value-types.html
>> +#[inline]
>> +fn format_value(input: &str) -> Result<String, DecodeError> {
>> +    let input = if let Some(input) = input.strip_prefix(" ") {
>> +        input
>> +    } else {
>> +        input
>> +    };
>> +
>> +    let mut res = String::with_capacity(input.len());
>> +
>> +    let mut last: usize = 0;
>> +
>> +    for (i, v) in input.as_bytes().iter().enumerate() {
>> +        if *v != b'\\' {
>> +            continue;
>> +        }
>> +
>> +        // edge case for //
>> +        if last > i {
>> +            continue;
>> +        }
>> +
>> +        // when there is an \ at the end
>> +        if input.len() <= i + 1 {
>> +            return Err(DecodeError::InvalidValue);
>> +        }
>> +
>> +        if last < i {
>> +            res.push_str(&input[last..i]);
>> +        }
>> +
>> +        last = i + 2;
>> +
>> +        match input.as_bytes()[i + 1] {
>> +            b's' => res.push(' '),
>> +            b'n' => res.push('\n'),
>> +            b't' => res.push('\t'),
>> +            b'r' => res.push('\r'),
>> +            b'\\' => res.push('\\'),
>> +            _ => {
>> +                return Err(DecodeError::InvalidValue);
>> +            }
>> +        }
>> +    }
>> +
>> +    if last < input.len() {
>> +        res.push_str(&input[last..input.len()]);
>> +    }
>> +
>> +    Ok(res)
>> +}
>> diff --git a/tools/mount-flatpak/src/main.rs b/tools/mount-flatpak/src/main.rs
>> new file mode 100644
>> index 0000000..6fc0556
>> --- /dev/null
>> +++ b/tools/mount-flatpak/src/main.rs
>> @@ -0,0 +1,288 @@
>> +// SPDX-FileCopyrightText: 2025 Alyssa Ross <hi@alyssa.is>
>> +// SPDX-License-Identifier: EUPL-1.2+
>> +
>> +//! Flatpak installations look like this:
>> +//!
>> +//! ```text
>> +//! flatpak/
>> +//! ├── app/
>> +//! │   └── org.gnome.TextEditor/
>> +//! │       ├── current -> x86_64/stable
>> +//! │       └── x86_64/
>> +//! │           └── stable/
>> +//! │               ├── 0029140121b39f5b7cf4d44fd46b0708eee67f395b5e1291628612a0358fb909/
>> +//! │               │   └── …
>> +//! │               └── active -> 0029140121b39f5b7cf4d44fd46b0708eee67f395b5e1291628612a0358fb909
>> +//! ├── db/
>> +//! ├── exports/
>> +//! │   └── …
>> +//! ├── repo
>> +//! │   ├── config
>> +//! │   ├── objects
>> +//! │   ├── tmp
>> +//! │   │   └── cache
>> +//! │   │       └── …
>> +//! │   └── …
>> +//! └── runtime
>> +//!     ├── org.gnome.Platform
>> +//!     │   └── x86_64
>> +//!     │       └── 49
>> +//!     │           ├── active -> bf6aa432cb310726f4ac0ec08cc88558619e1d4bd4b964e27e95187ecaad5400
>> +//!     │           └── bf6aa432cb310726f4ac0ec08cc88558619e1d4bd4b964e27e95187ecaad5400
>> +//!     │               └── …
>> +//!     └── …
>> +//! ```
>> +//!
>> +//! The purpose of this program is to use bind mounts to construct a
>> +//! Flatpak installation containing only a single application and
>> +//! runtime, which can be passed through to a VM without exposing
>> +//! other installed applications.
>> +
>> +mod keyfile;
>> +mod metadata;
>> +
>> +use std::borrow::Cow;
>> +use std::env::{ArgsOs, args_os};
>> +use std::ffi::OsStr;
>> +use std::io;
>> +use std::os::unix::prelude::*;
>> +use std::path::{Path, PathBuf};
>> +use std::process::exit;
>> +
>> +use pathrs::Root;
>> +use pathrs::flags::{OpenFlags, ResolverFlags};
>> +use rustix::fs::{CWD, FileType, fstat};
>> +use rustix::mount::{MoveMountFlags, OpenTreeFlags, move_mount, open_tree};
>> +
>> +use metadata::extract_runtime;
>> +
>> +fn ex_usage() -> ! {
>> +    eprintln!("Usage: mount-flatpak userdata installation app");
>> +    exit(1);
>> +}
>> +
>> +fn mount_commit(
>> +    source_commit: &dyn AsFd,
>> +    target_installation: &Root,
>> +    path: &Path,
>> +) -> Result<(), String> {
>> +    let source_commit_tree = open_tree(
>> +        source_commit,
>> +        "",
>> +        OpenTreeFlags::AT_EMPTY_PATH
>> +            | OpenTreeFlags::OPEN_TREE_CLONE
>> +            | OpenTreeFlags::OPEN_TREE_CLOEXEC
>> +            | OpenTreeFlags::AT_RECURSIVE,
>> +    )
>> +    .map_err(|e| format!("cloning source commit tree: {e}"))?;
>> +    let target_commit_dir = target_installation
>> +        .mkdir_all(path, &PermissionsExt::from_mode(0o700))
>> +        .map_err(|e| format!("creating target commit directory: {e}"))?;
> 
> Does this check for path being absolute?  I don't know how Rust
> handles joining a relative path to an absolute one.
> 
>> +    move_mount(
>> +        source_commit_tree,
>> +        "",
>> +        target_commit_dir,
>> +        "",
>> +        MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH | MoveMountFlags::MOVE_MOUNT_T_EMPTY_PATH,
>> +    )
>> +    .map_err(|e| format!("mounting commit: {e}"))
>> +}
>> +
>> +fn run(mut args: ArgsOs) -> Result<(), String> {
>> +    let Some(user_data_path) = args.next().map(PathBuf::from) else {
>> +        ex_usage();
>> +    };
>> +    let Some(installation_path) = args.next().map(PathBuf::from) else {
>> +        ex_usage();
>> +    };
>> +    let Some(app) = args.next() else {
>> +        ex_usage();
>> +    };
>> +    if args.next().is_some() {
>> +        ex_usage();
>> +    }
>> +
>> +    let mut user_data =
>> +        Root::open(&user_data_path).map_err(|e| format!("opening user data partition: {e}"))?;
>> +    user_data.set_resolver_flags(ResolverFlags::NO_SYMLINKS);
>> +
>> +    let mut source_installation_dir = user_data
>> +        .open_subpath(&installation_path, OpenFlags::O_PATH)
>> +        .map(Root::from_fd)
>> +        .map_err(|e| format!("opening source flatpak installation: {e}"))?;
>> +    source_installation_dir.set_resolver_flags(ResolverFlags::NO_SYMLINKS);
>> +
>> +    std::fs::create_dir("flatpak")
>> +        .map_err(|e| format!("creating target flatpak installation: {e}"))?;
>> +
>> +    let target_installation_dir = open_tree(
>> +        CWD,
>> +        "flatpak",
>> +        OpenTreeFlags::OPEN_TREE_CLONE
>> +            | OpenTreeFlags::OPEN_TREE_CLOEXEC
>> +            | OpenTreeFlags::AT_RECURSIVE
>> +            | OpenTreeFlags::AT_SYMLINK_NOFOLLOW,
>> +    )
>> +    .map_err(|e| format!("opening target flatpak installation: {e}"))?;
>> +    let mut target_installation_dir = Root::from_fd(target_installation_dir);
>> +    target_installation_dir.set_resolver_flags(ResolverFlags::NO_SYMLINKS);
>> +
>> +    let mut full_app_path = installation_path.join("app");
>> +    full_app_path.push(&app);
>> +    full_app_path.push("current");
>> +    let arch_and_branch = source_installation_dir
>> +        .readlink(&full_app_path)
>> +        .map_err(|e| format!("reading current app arch and branch: {e}"))?;
>> +    let mut components = arch_and_branch.components();
>> +    let arch = components.next().unwrap().as_os_str();
> 
> Still panics if there is no next component.
> 
>> +    let branch = components.as_path().as_os_str();
>> +    if branch.is_empty() {
>> +        return Err("can't infer branch from \"current\" link".to_string());
>> +    }
>> +
>> +    full_app_path.pop();
>> +    full_app_path.push(&arch_and_branch);
>> +    full_app_path.push("active");
>> +    let commit = source_installation_dir
>> +        .readlink(&full_app_path)
>> +        .map_err(|e| format!("reading active app commit: {e}"))?
>> +        .into_os_string();
> 
> This can (and should) be moved into mount_commit().
> 
>> +    full_app_path.pop();
>> +    full_app_path.push(&commit);
> 
> I strongly recommend validating the commit here.  This avoids Rust’s
> stdlib path functions potentially mishandling absolute paths, ".",
> or ".." (by popping off the last components).  I don’t know if
> they *do* mishandle it, but validation is obviously correct, and not
> validating isn’t.
> 
>> +    let source_app_dir = source_installation_dir
>> +        .resolve(&full_app_path)
>> +        .map_err(|e| format!("opening source app directory: {e}"))?;
>> +
>> +    let metadata = source_installation_dir
>> +        .resolve(full_app_path.join("metadata"))
>> +        .map_err(|e| format!("resolving app metadata: {e}"))?;
>> +
>> +    let metadata_stat =
>> +        fstat(&metadata).map_err(|e| format!("checking app metadata is a regular file: {e}"))?;
>> +    let metadata_type = FileType::from_raw_mode(metadata_stat.st_mode);
>> +    if !metadata_type.is_file() {
>> +        let e = format!("type of app metadata is {metadata_type:?}, not RegularFile");
>> +        return Err(e);
>> +    }
>> +    let metadata = metadata
>> +        .reopen(OpenFlags::O_RDONLY)
>> +        .map_err(|e| format!("opening app metadata: {e}"))?;
>> +
>> +    let runtime =
>> +        extract_runtime(metadata).map_err(|e| format!("reading runtime from metadata: {e}"))?;
>> +
>> +    let mut full_runtime_path = installation_path.join("runtime");
>> +    full_runtime_path.push(runtime);
>> +    full_runtime_path.push("active");
>> +    let runtime_commit = source_installation_dir
>> +        .readlink(&full_runtime_path)
>> +        .map_err(|e| format!("reading active runtime commit: {e}"))?
>> +        .into_os_string();
>> +
>> +    full_runtime_path.pop();
>> +    full_runtime_path.push(&runtime_commit);
>> +    let source_runtime_dir = source_installation_dir
>> +        .resolve(&full_runtime_path)
>> +        .map_err(|e| format!("opening source runtime directory: {e}"))?;
> 
> Same comments as above.  Also, does the error contain the path name?
> I'm guessing it doesn’t, but it would be best to check that.
> 
>> +    mount_commit(&source_app_dir, &target_installation_dir, &full_app_path)?;
>> +    mount_commit(
>> +        &source_runtime_dir,
>> +        &target_installation_dir,
>> +        &full_runtime_path,
>> +    )?;
>> +
>> +    target_installation_dir
>> +        .mkdir_all("repo/objects", &PermissionsExt::from_mode(0o700))
>> +        .map_err(|e| format!("creating repo/objects: {e}"))?;
>> +    target_installation_dir
>> +        .mkdir_all("repo/tmp/cache", &PermissionsExt::from_mode(0o700))
>> +        .map_err(|e| format!("creating repo/tmp/cache: {e}"))?;
>> +    let config_target = target_installation_dir
>> +        .create_file(
>> +            "repo/config",
>> +            OpenFlags::O_WRONLY | OpenFlags::O_CLOEXEC,
>> +            &PermissionsExt::from_mode(0o700),
>> +        )
>> +        .map_err(|e| format!("creating repo/config: {e}"))?;
>> +    let config_source_path = env!("MOUNT_FLATPAK_CONFIG_PATH");
>> +    let config_source = open_tree(
>> +        CWD,
>> +        config_source_path,
>> +        OpenTreeFlags::OPEN_TREE_CLONE | OpenTreeFlags::OPEN_TREE_CLOEXEC,
>> +    )
>> +    .map_err(|e| format!("opening {config_source_path}: {e}"))?;
>> +    move_mount(
>> +        config_source,
>> +        "",
>> +        config_target,
>> +        "",
>> +        MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH | MoveMountFlags::MOVE_MOUNT_T_EMPTY_PATH,
>> +    )
>> +    .map_err(|e| format!("mounting config: {e}"))?;
>> +
>> +    let mut attr = libc::mount_attr {
>> +        attr_clr: libc::MOUNT_ATTR_NOSYMFOLLOW,
>> +        attr_set: libc::MOUNT_ATTR_RDONLY | libc::MOUNT_ATTR_NODEV,
>> +        propagation: libc::MS_SLAVE,
>> +        userns_fd: 0,
>> +    };
>> +    let empty = b"\0";
>> +    // SAFETY: we pass a valid FD, valid C string, and a valid mutable pointer with the
>> +    // correct size.
>> +    unsafe {
>> +        let r = libc::syscall(
>> +            libc::SYS_mount_setattr,
>> +            target_installation_dir.as_fd().as_raw_fd() as libc::c_long,
>> +            empty.as_ptr() as *const libc::c_char,
>> +            (libc::AT_EMPTY_PATH | libc::AT_RECURSIVE) as libc::c_long,
>> +            &mut attr as *mut libc::mount_attr,
>> +            size_of::<libc::mount_attr>() as libc::c_long,
>> +        );
>> +        if r == -1 {
>> +            return Err(format!(
>> +                "setting target mount attributes: {}",
>> +                io::Error::last_os_error()
>> +            ));
>> +        }
>> +    }
>> +    move_mount(
>> +        target_installation_dir,
>> +        "",
>> +        CWD,
>> +        "flatpak",
>> +        MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH,
>> +    )
>> +    .map_err(|e| format!("mounting target installation dir: {e}"))?;
>> +
>> +    std::fs::create_dir("params").map_err(|e| format!("creating params directory: {e}"))?;
>> +    std::fs::write("params/id", app.as_bytes()).map_err(|e| format!("writing params/id: {e}"))?;
>> +    std::fs::write("params/commit", commit.as_bytes())
>> +        .map_err(|e| format!("writing params/commit: {e}"))?;
>> +    std::fs::write("params/arch", arch.as_bytes())
>> +        .map_err(|e| format!("writing params/arch: {e}"))?;
>> +    std::fs::write("params/branch", branch.as_bytes())
>> +        .map_err(|e| format!("writing params/branch: {e}"))?;
>> +    std::fs::write("params/runtime-commit", runtime_commit.as_bytes())
>> +        .map_err(|e| format!("writing params/runtime-commit: {e}"))?;
>> +
>> +    Ok(())
>> +}
>> +
>> +fn main() {
>> +    let mut args = args_os();
>> +
>> +    let prog_name = args
>> +        .next()
>> +        .as_ref()
>> +        .map(Path::new)
>> +        .and_then(Path::file_name)
>> +        .map_or(Cow::Borrowed("mount-flatpak"), OsStr::to_string_lossy)
>> +        .into_owned();
>> +
>> +    if let Err(e) = run(args) {
>> +        eprintln!("{prog_name}: {e}");
>> +        exit(1);
>> +    }
>> +}
>> diff --git a/tools/mount-flatpak/src/metadata.rs b/tools/mount-flatpak/src/metadata.rs
>> new file mode 100644
>> index 0000000..dfc05b1
>> --- /dev/null
>> +++ b/tools/mount-flatpak/src/metadata.rs
>> @@ -0,0 +1,19 @@
>> +// SPDX-License-Identifier: EUPL-1.2+
>> +// SPDX-FileCopyrightText: 2025 Alyssa Ross <hi@alyssa.is>
>> +
>> +use std::fs::File;
>> +use std::io::read_to_string;
>> +
>> +use crate::keyfile::parse;
>> +
>> +pub fn extract_runtime(mut metadata: File) -> Result<String, String> {
>> +    let metadata = read_to_string(&mut metadata).map_err(|e| e.to_string())?;
> 
> Is this going to be in the VM's cgroup?
> 
>> +    let group = parse(&metadata).map_err(|e| e.to_string())?;
>> +    let application = group
>> +        .get("Application")
>> +        .ok_or_else(|| "Application group missing".to_string())?;
>> +    Ok(application
>> +        .get("runtime")
>> +        .ok_or_else(|| "runtime property missing".to_string())?
>> +        .clone())
>> +}

Nevermind, I didn't read your previous email before sending this.  Ignore it.

https://spectrum-os.org/lists/archives/spectrum-devel/87y0nmv2v4.fsf@alyssa.is/T/#u
addresses all of the comments.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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