[Virtio-fs] [PATCH v2] fuse: invalidate inode attr in writeback cache mode

[Miklos Szeredi]

On Tue, May 12, 2020 at 4:29 AM Eryu Guan <eguan at linux.alibaba.com> wrote:
>
> Under writeback mode, inode->i_blocks is not updated, making utils du
> read st.blocks as 0.
>
> For example, when using virtiofs (cache=always & nondax mode) with
> writeback_cache enabled, writing a new file and check its disk usage
> with du, du reports 0 usage.
>
>   # uname -r
>   5.6.0-rc6+
>   # mount -t virtiofs virtiofs /mnt/virtiofs
>   # rm -f /mnt/virtiofs/testfile
>
>   # create new file and do extend write
>   # xfs_io -fc "pwrite 0 4k" /mnt/virtiofs/testfile
>   wrote 4096/4096 bytes at offset 0
>   4 KiB, 1 ops; 0.0001 sec (28.103 MiB/sec and 7194.2446 ops/sec)
>   # du -k /mnt/virtiofs/testfile
>   0               <==== disk usage is 0
>   # stat -c %s,%b /mnt/virtiofs/testfile
>   4096,0          <==== i_size is correct, but st_blocks is 0
>
> Fix it by invalidating attr in fuse_flush(), so we get up-to-date attr
> from server on next getattr.

Thanks, applied.

I started thinking: why is fuse_flush() only writing out dirty pages
if fc->no_flush is false?   It just doesn't make sense...  But that's
an independent bug, and I'll do a separate patch for that.

Thanks,
Miklos