On Wed 25-10-17 09:23:22, Dave Chinner wrote: > On Tue, Oct 24, 2017 at 05:24:14PM +0200, Jan Kara wrote: > > From: Christoph Hellwig <hch@xxxxxx> > > > > Return IOMAP_F_DIRTY from xfs_file_iomap_begin() when asked to prepare > > blocks for writing and the inode is pinned, and has dirty fields other > > than the timestamps. > > That's "fdatasync dirty", not "fsync dirty". Correct. > IOMAP_F_DIRTY needs a far better description of it's semantics than > "/* block mapping is not yet on persistent storage */" so we know > exactly what filesystems are supposed to be implementing here. I > suspect that what it really is meant to say is: > > /* > * IOMAP_F_DIRTY indicates the inode has uncommitted metadata to > * written data and requires fdatasync to commit to persistent storage. > */ I'll update the comment. Thanks! > [....] > > > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c > > index f179bdf1644d..b43be199fbdf 100644 > > --- a/fs/xfs/xfs_iomap.c > > +++ b/fs/xfs/xfs_iomap.c > > @@ -33,6 +33,7 @@ > > #include "xfs_error.h" > > #include "xfs_trans.h" > > #include "xfs_trans_space.h" > > +#include "xfs_inode_item.h" > > #include "xfs_iomap.h" > > #include "xfs_trace.h" > > #include "xfs_icache.h" > > @@ -1086,6 +1087,10 @@ xfs_file_iomap_begin( > > trace_xfs_iomap_found(ip, offset, length, 0, &imap); > > } > > > > + if ((flags & IOMAP_WRITE) && xfs_ipincount(ip) && > > + (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP)) > > + iomap->flags |= IOMAP_F_DIRTY; > > This is the very definition of an inode that is "fdatasync dirty". > > Hmmmm, shouldn't this also be set for read faults, too? No, read faults don't need to set IOMAP_F_DIRTY since user cannot write any data to the page which he'd then like to be persistent. The only reason why I thought it could be useful for a while was that it would be nice to make MAP_SYNC mapping provide the guarantee that data you see now is the data you'll see after a crash but we cannot provide that guarantee for RO mapping anyway if someone else has the page mapped as well. So I just decided not to return IOMAP_F_DIRTY for read faults. But now that I look at XFS implementation again, it misses handling of VM_FAULT_NEEDSYNC in xfs_filemap_pfn_mkwrite() (ext4 gets this right). I'll fix this by using __xfs_filemap_fault() for xfs_filemap_pfn_mkwrite() as well since it mostly duplicates it anyway... Thanks for inquiring! Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
