On Mon, Feb 05, 2024 at 12:58:30PM +0000, John Garry wrote:
> On 02/02/2024 17:57, Darrick J. Wong wrote:
> > On Wed, Jan 24, 2024 at 02:26:41PM +0000, John Garry wrote:
> > > Add a flag indicating that a regular file is enabled for atomic writes.
> >
> > This is a file attribute that mirrors an ondisk inode flag. Actual
> > support for untorn file writes (for now) depends on both the iflag and
> > the underlying storage devices, which we can only really check at statx
> > and pwrite time. This is the same story as FS_XFLAG_DAX, which signals
> > to the fs that we should try to enable the fsdax IO path on the file
> > (instead of the regular page cache), but applications have to query
> > STAT_ATTR_DAX to find out if they really got that IO path.
>
> To be clear, are you suggesting to add this info to the commit message?
That and a S_ATOMICW flag for the inode that triggers the proposed
STAT_ATTR_ATOMICWRITES flag.
> > "try to enable atomic writes", perhaps? >
> > (and the comment for FS_XFLAG_DAX ought to read "try to use DAX for IO")
>
> To me that sounds like "try to use DAX for IO, and, if not possible, fall
> back on some other method" - is that reality of what that flag does?
As hch said, yes.
--D
> Thanks,
> John
>
> >
> > --D
> >
> > >
> > > Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
> > > ---
> > > include/uapi/linux/fs.h | 1 +
> > > 1 file changed, 1 insertion(+)
> > >
> > > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> > > index a0975ae81e64..b5b4e1db9576 100644
> > > --- a/include/uapi/linux/fs.h
> > > +++ b/include/uapi/linux/fs.h
> > > @@ -140,6 +140,7 @@ struct fsxattr {
> > > #define FS_XFLAG_FILESTREAM 0x00004000 /* use filestream allocator */
> > > #define FS_XFLAG_DAX 0x00008000 /* use DAX for IO */
> > > #define FS_XFLAG_COWEXTSIZE 0x00010000 /* CoW extent size allocator hint */
> > > +#define FS_XFLAG_ATOMICWRITES 0x00020000 /* atomic writes enabled */
> > > #define FS_XFLAG_HASATTR 0x80000000 /* no DIFLAG for this */
> > > /* the read-only stuff doesn't really belong here, but any other place is
> > > --
> > > 2.31.1
> > >
> > >
>
>
