[pbs-devel] applied: [PATCH proxmox-backup] backup-client: mount: fix read of larger files

[Fabian Grünbichler]

with a comment added and a slight rewording of the commit message, as
triggering the bug doesn't really truncate files, it overwrites parts of 
them with all-zero blocks at different offsets.

On September 2, 2022 9:21 am, Dominik Csapak wrote:
> fuse_lowlevel.h says about read:
> 
>  Read should send exactly the number of bytes requested except
>  on EOF or error, otherwise the rest of the data will be
>  substituted with zeroes.
> 
> but we simply forwarded the bytes we got from 'read_at'. The result was
> that larger files were truncated as soon as read_at returned not the
> exact number of bytes requested.
> 
> To fix that, loop over 'read_at' until our buffer is full, or we read
> 0 bytes, indicating EOF.
> 
> reported in the forum:
> https://forum.proxmox.com/threads/proxmox-backup-client-mounting-a-pxar-archive-gives-truncated-files.114447/
> 
> Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
> ---
> tested with some larger files (>100MiB), before the patch, a 'cmp' with the
> original would always fail, after it worked like expected
> 
>  pbs-client/src/pxar/fuse.rs | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/pbs-client/src/pxar/fuse.rs b/pbs-client/src/pxar/fuse.rs
> index e9e1b6f3..f2ce6a43 100644
> --- a/pbs-client/src/pxar/fuse.rs
> +++ b/pbs-client/src/pxar/fuse.rs
> @@ -566,8 +566,17 @@ impl SessionImpl {
>          let file = self.get_lookup(inode)?;
>          let content = self.open_content(&file)?;
>          let mut buf = vec::undefined(len);
> -        let got = content.read_at(&mut buf, offset).await?;
> -        buf.truncate(got);
> +        let mut pos = 0;
> +        loop {
> +            let got = content
> +                .read_at(&mut buf[pos..], offset + pos as u64)
> +                .await?;
> +            pos += got;
> +            if got == 0 || pos >= len {
> +                break;
> +            }
> +        }
> +        buf.truncate(pos);
>          Ok(buf)
>      }
>  
> -- 
> 2.30.2
> 
> 
> 
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