Re: [PATCH v2 3/9] smb/client: handle smb2_set_sparse() failure in EOF-extending fallocate

[hehuiwen <huiwen.he@linux.dev>]

Hi Steve,

Yes, that is possible. I checked ext4, XFS and btrfs with examples like:

         truncate -s 1M file
         fallocate -n -o 2M -l 1M file
         filefrag -v file

and:

         truncate -s 1M file
         fallocate -o 2M -l 1M file
         filefrag -v file

With FALLOC_FL_KEEP_SIZE, the file size stays at 1M while the range
[2M, 3M) is preallocated. Without FALLOC_FL_KEEP_SIZE, the file size 
grows to 3M, but the filesystems still only allocate the requested
range [2M, 3M). Holes before that range are not removed.

Patch 3 only changes the error handling around the existing
smb2_set_sparse(..., false) call. I agree that clearing the sparse
attribute is not a general byte-range allocation mechanism.

Patch 9 handles the sparse EOF-adjacent case differently: small ranges 
are allocated by writing zeroes only to the requested range, and larger 
ranges remain unsupported. That avoids clearing the sparse attribute
for this case.

Thanks,
Huiwen


在 2026/6/24 10:48, Steve French 写道:
> Would it be possible in Linux to have a sparse file but still with
> space reserved beyond end of file?  In other words are there cases
> where you could have a file with holes in it in Linux which still
> fallocated beyond end of file.  What happens to ext4, xfs, btrfs if
> you try that?  Does fallocate beyond of file remove all holes in a
> (sparse) file?