Re: [PATCH 4/7] xfs: Implement fallocate query support mode

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Sep 18, 2017 at 05:52:24PM +0200, Lukas Czerner wrote:
> Return all fallcoate modes supported by xfs file system.
> 
> Cc: linux-xfs@vger.kernel.org
> Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> ---
>  fs/xfs/xfs_file.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index ebdd0bd..85e06c6 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -746,7 +746,8 @@ xfs_file_write_iter(
>  #define	XFS_FALLOC_FL_SUPPORTED						\
>  		(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |		\
>  		 FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |	\
> -		 FALLOC_FL_INSERT_RANGE | FALLOC_FL_UNSHARE_RANGE)
> +		 FALLOC_FL_INSERT_RANGE | FALLOC_FL_UNSHARE_RANGE |	\
> +		 FALLOC_FL_QUERY_SUPPORT | FALLOC_FL_PREALLOC_RANGE)
>  
>  STATIC long
>  xfs_file_fallocate(
> @@ -768,6 +769,9 @@ xfs_file_fallocate(
>  	if (mode & ~XFS_FALLOC_FL_SUPPORTED)
>  		return -EOPNOTSUPP;
>  
> +	if (mode & FALLOC_FL_QUERY_SUPPORT)
> +		return XFS_FALLOC_FL_SUPPORTED;

Urk, manpage update describing the goals of the query interface and how
this is supposed to work is needed.

Are we required to return only the mode flags that would reasonably be
expected to work on this file, or the fs in general?  Do we return zero
if the file is immutable (I guess the fd has to be O_RDONLY?) or if the
fs is readonly?

And like hch said, why not {f,}pathconf?

--D

> +
>  	xfs_ilock(ip, iolock);
>  	error = xfs_break_layouts(inode, &iolock);
>  	if (error)
> -- 
> 2.7.5
> 
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