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SubjectRe: [PATCH 03/17] vfs: Remove syncing from generic_file_direct_write() and generic_file_buffered_write()
On Wed, Aug 19, 2009 at 06:04:30PM +0200, Jan Kara wrote:
> generic_file_direct_write() and generic_file_buffered_write() called
> generic_osync_inode() if it was called on O_SYNC file or IS_SYNC inode. But
> this is superfluous since generic_file_aio_write() does the syncing as well.
> Also XFS and OCFS2 which call these functions directly handle syncing
> themselves. So let's have a single place where syncing happens:
> generic_file_aio_write().

Yeah, this is something that never made any sense to me.

> @@ -2187,20 +2187,7 @@ generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
> }
> *ppos = end;
> }
> -
> - /*
> - * Sync the fs metadata but not the minor inode changes and
> - * of course not the data as we did direct DMA for the IO.
> - * i_mutex is held, which protects generic_osync_inode() from
> - * livelocking. AIO O_DIRECT ops attempt to sync metadata here.
> - */
> out:
> - if ((written >= 0 || written == -EIOCBQUEUED) &&
> - ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
> - int err = generic_osync_inode(inode, mapping, OSYNC_METADATA);
> - if (err < 0)
> - written = err;
> - }
> return written;

Here we check (written >= 0 || written == -EIOCBQUEUED), but
generic_file_aio_write only cares about positive return values. We
defintively do have a change here for partial AIO requests. The
question is if the previous behaviour made in sense. If do have an
O_SYNC aio+dio request we would have to flush out the metadata after the
request has completed and not here.
> @@ -2343,16 +2328,6 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
> if (likely(status >= 0)) {
> written += status;
> *ppos = pos + status;
> -
> - /*
> - * For now, when the user asks for O_SYNC, we'll actually give
> - * O_DSYNC
> - */
> - if (unlikely((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
> - if (!a_ops->writepage || !is_sync_kiocb(iocb))
> - status = generic_osync_inode(inode, mapping,
> - OSYNC_METADATA|OSYNC_DATA);
> - }
> }

No problem with -EIOCBQUEUED here, but we change from doing
generic_osync_inode with OSYNC_DATA which does a full writeout of the
data to sync_page_range which only does the range writeout here. That
should be fine (as we only need to sync that range), but should probably
be documented in the patch description.


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