Commits on Oct 11, 2024

1. Fix parallel downloads of the same image …

   When starting multiple vms in parallel using the same uncached yet
   image, we downloaded the data to the same temporary file (data.tmp) and
   wrote metadata to the same files (url, time, type, {digest}.digest). We
   could fail in many ways:
   
   - One process removes the cache directory when another tries to rename a
     temporary file to the destination file.
   - One process fails to remove the cache directory since another process
     started to download and the directory is not empty.
   - Corrupting data when writing to the same file from multiple processes.
     Mostly likely when writing downloaded data.
   
   Fixes:
   
   - Do not remove the cache directory before the download. This avoids the
     failing to remove non-empty directory, and failure to rename a
     temporary file.
   - Write all data to temporary files, replacing the destination file when
     the write is complete. This avoid corrupted data.
   - Do not remove destination file when creating a new temporary file or
     renaming since creating a file truncate existing file and renaming
     replace it.
   
   Issues:
   
   - On windows os.Rename is not atomic, but it should work when using
     NTFS.
   - On failures we may have lefover temporary files ({name}.tmp.{pid}).
   
   Fixes lima-vm#2722
   
   Signed-off-by: Nir Soffer <[email protected]>

   

   nirs committed Oct 11, 2024
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