Don't fail on creation of `sdist-vX/.git` if it already exists by konstin · Pull Request #17825 · astral-sh/uv

konstin · 2026-02-03T10:12:27Z

Step 1 of N for readonly cache support. Moves the error message for LLM sandboxes from sdist-vX/.git to:

error: Could not acquire lock
    Caused by: Could not create temporary file
    Caused by: Read-only file system (os error 30  at path "/home/konsti/.cache/uv/.tmpfvc4gV"

zanieb · 2026-02-03T14:46:54Z

crates/uv-cache/src/lib.rs

+            fs_err::OpenOptions::new()
+                .create(true)
+                .write(true)
+                .open(phony_git)?;


Does this return a different error type with create(true) such that we can tell if it exists already without an extra syscall?

(per create(true) I don't think the title of this pull request is accurate, we shouldn't be recreating it already)

I wonder why we even open it for writing if we don't write to it?

The information is not preserved: https://github.com/astral-sh/uv/pull/1782/changes

I tried fs_err::OpenOptions::new().create_new(true).open(phony_git) and fs_err::OpenOptions::new().create(true).open(phony_git) but the error type isn't structured, we can't detect it reliably:

[crates/uv-cache/src/lib.rs:455:9] output = Err( Custom { kind: InvalidInput, error: Error { kind: OpenFile, source: Custom { kind: InvalidInput, error: "creating or truncating a file requires write or append access", }, path: "/home/konsti/.cache/uv/sdists-v9/.git", }, }, ) error: Failed to initialize cache at `/home/konsti/.cache/uv` Caused by: failed to open file `/home/konsti/.cache/uv/sdists-v9/.git`: creating or truncating a file requires write or append access

Turns out the reason is we fail if we don't have .write(true).

zanieb · 2026-02-04T13:31:33Z

Unfortunately we can still hit the sandbox error in a race condition, which... seems rare but would be nice to avoid if we can. Could we just check if the file exists after we see an error then ignore the error if so? Also I presume if the file is missing we get a different error than if it exists but is read only?

konstin · 2026-02-04T16:01:37Z

If the cache directory doesn't exist you get earlier failures, we fail to create /home/konsti/.cache/uv or one of the other files. I'm afraid I don't have any better as how to avoid the extra check, the sandbox doesn't seem to return properly distinguished error messages. While the TOCTOU is a bad practice, the file is "touch only" (expect for cache clean), this doesn't seem like something that could create an observable bug.

No cache:

● Bash(uv-debug pip install tqdm -vv)                                                                                                                                                                                                                                                                                                                 
  ⎿  Error: Exit code 2                                                                                                                                                                                                                                                                                                                             
     DEBUG uv 0.9.29+4 (a014ae0a2 2026-02-04)                                                                                                                                                                                                                                                                                                         
     TRACE Error trace: Failed to initialize cache at `/home/konsti/.cache/uv`
                                                                                                                                                                                                                                                                                                                                                      
     Caused by:                                                                                                                                                                                                                                                                                                                                       
         failed to create directory `/home/konsti/.cache/uv`: Read-only file system (os error 30)                                                                                                                                                                                                                                                   
     error: Failed to initialize cache at `/home/konsti/.cache/uv`                                                                                                                                                                                                                                                                                    
       Caused by: failed to create directory `/home/konsti/.cache/uv`: Read-only file system (os error 30)

Cache dir exists, but is empty:

● Bash(uv-debug pip install tqdm -vv)                                                                                                                                                                                                                                                                                                                 
  ⎿  Error: Exit code 2                                                                                                                                                                                                                                                                                                                             
     DEBUG uv 0.9.29+4 (a014ae0a2 2026-02-04)                                                                                                                                                                                                                                                                                                         
     TRACE Error trace: Failed to initialize cache at `/home/konsti/.cache/uv`
                                                                                                                                                                                                                                                                                                                                                      
     Caused by:                                                                                                                                                                                                                                                                                                                                       
         failed to open file `/home/konsti/.cache/uv/CACHEDIR.TAG`: Read-only file system (os error 30)                                                                                                                                                                                                                                             
     error: Failed to initialize cache at `/home/konsti/.cache/uv`                                                                                                                                                                                                                                                                                    
       Caused by: failed to open file `/home/konsti/.cache/uv/CACHEDIR.TAG`: Read-only file system (os error 30)

Whether ~/.cache/uv/sdists-v9/.git exists doesn't seem to change the error message, I suspect :

● Bash(uv-debug pip install tqdm -vv)
  ⎿  Error: Exit code 2
     DEBUG uv 0.9.29+4 (a014ae0a2 2026-02-04)
     [crates/uv-cache/src/lib.rs:451:9] fs_err::OpenOptions::new().create(true).write(true).open(&phony_git) = Err(
         Custom {
             kind: ReadOnlyFilesystem,
             error: Error {
                 kind: OpenFile,
                 source: Os {
                     code: 30,
                     kind: ReadOnlyFilesystem,
                     message: "Read-only file system",
                 },
                 path: "/home/konsti/.cache/uv/sdists-v9/.git",
             },
         },
     )
     TRACE Error trace: Could not acquire lock

● Bash(uv-debug pip install tqdm -vv)                                                                                                                                                                                                                                                                                                                 
  ⎿  Error: Exit code 2                                                                                                                                                                                                                                                                                                                             
     DEBUG uv 0.9.29+4 (a014ae0a2 2026-02-04)                                                                                                                                                                                                                                                                                                         
     [crates/uv-cache/src/lib.rs:451:9] fs_err::OpenOptions::new().create(true).write(true).open(&phony_git) = Err(
         Custom {                                                                                                                                                                                                                                                                                                                                     
             kind: ReadOnlyFilesystem,                                                                                                                                                                                                                                                                                                                
             error: Error {                                                                                                                                                                                                                                                                                                                         
                 kind: OpenFile,                                                                                                                                                                                                                                                                                                                      
                 source: Os {                                                                                                                                                                                                                                                                                                                       
                     code: 30,                                                                                                                                                                                                                                                                                                                      
                     kind: ReadOnlyFilesystem,                                                                                                                                                                                                                                                                                                      
                     message: "Read-only file system",
                 },
                 path: "/home/konsti/.cache/uv/sdists-v9/.git",
             },
         },
     )

zanieb · 2026-02-04T18:09:01Z

While the TOCTOU is a bad practice, the file is "touch only" (expect for cache clean), this doesn't seem like something that could create an observable bug.

The observable bug would be the same sandbox error that you're trying to fix.

Don't we have a ReadOnlyFilesystem error? Why can't we check that the file exists after we see that error instead of before?

konstin · 2026-02-05T10:15:37Z

Can you describe the order of events that you see for this TUCTOU bug? Does it introduce any additional failure paths?

zanieb · 2026-02-05T14:55:23Z

No it doesn't introduce any new failure paths, but I don't understand the resistance to making the small change needed to avoid it? Do you want me to draft what I'm saying?

The TOCTOU is

A: Checks if the file exists -> no
B: Checks if the file exists -> no
B: Creates file
A: Fails with the existing error

Where B has cache write permissions (i.e., not sandboxed), and A is sandboxed.

zanieb · 2026-02-05T15:04:58Z

e.g., why is 398a979 worse?

konstin · 2026-02-06T10:49:48Z

I see, I don't think we can properly handle races between unsandboxed and sandboxed uv processes more generally (the sandboxed version fails or passes depending on the timing), but I agree that 398a979 is better code.

zanieb

Yeah I agree the situation will be hard to handle robustly

This MR contains the following updates: | Package | Update | Change | |---|---|---| | [uv](https://github.com/astral-sh/uv) | patch | `0.10.0` → `0.10.2` | MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot). **Proposed changes to behavior should be submitted there as MRs.** --- ### Release Notes <details> <summary>astral-sh/uv (uv)</summary> ### [`v0.10.2`](https://github.com/astral-sh/uv/blob/HEAD/CHANGELOG.md#0102) [Compare Source](astral-sh/uv@0.10.1...0.10.2) Released on 2026-02-10. ##### Enhancements - Deprecate unexpected ZIP compression methods ([#17946](astral-sh/uv#17946)) ##### Bug fixes - Fix `cargo-install` failing due to missing `uv-test` dependency ([#17954](astral-sh/uv#17954)) ### [`v0.10.1`](https://github.com/astral-sh/uv/blob/HEAD/CHANGELOG.md#0101) [Compare Source](astral-sh/uv@0.10.0...0.10.1) Released on 2026-02-10. ##### Enhancements - Don't panic on metadata read errors ([#17904](astral-sh/uv#17904)) - Skip empty workspace members instead of failing ([#17901](astral-sh/uv#17901)) - Don't fail creating a read-only `sdist-vX/.git` if it already exists ([#17825](astral-sh/uv#17825)) ##### Documentation - Suggest `uv python update-shell` over `uv tool update-shell` in Python docs ([#17941](astral-sh/uv#17941)) </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this MR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this MR, check this box --- This MR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).

konstin added the enhancement New feature or improvement to existing functionality label Feb 3, 2026

zanieb reviewed Feb 3, 2026

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konstin had a problem deploying to uv-test-publish February 3, 2026 18:38 — with GitHub Actions Failure

konstin temporarily deployed to uv-test-publish February 3, 2026 21:04 — with GitHub Actions Inactive

konstin force-pushed the konsti/git-readonly branch from 42927fd to a014ae0 Compare February 4, 2026 15:01

konstin force-pushed the konsti/git-readonly branch from a014ae0 to c720cf2 Compare February 6, 2026 10:28

Don't recreate sdist-vX/.git if it already exists

88fb47a

konstin force-pushed the konsti/git-readonly branch from c720cf2 to 88fb47a Compare February 6, 2026 10:50

zanieb changed the title ~~Don't recreate sdist-vX/.git if it already exists~~ Don't fail on creation of sdist-vX/.git if it already exists Feb 6, 2026

zanieb approved these changes Feb 6, 2026

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konstin merged commit 0dbeb4c into main Feb 6, 2026
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konstin deleted the konsti/git-readonly branch February 6, 2026 13:46

BrewTestBot mentioned this pull request Feb 10, 2026

uv 0.10.1 Homebrew/homebrew-core#266742

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