On 4/26/22 3:54 PM, Dave Chinner wrote:
> On Tue, Apr 26, 2022 at 10:43:23AM -0700, Stefan Roesch wrote:
>> This adds the async buffered write support to the iomap layer of XFS. If
>> a lock cannot be acquired or additional reads need to be performed, the
>> request will return -EAGAIN in case this is an async buffered write request.
>>
>> Signed-off-by: Stefan Roesch <shr@xxxxxx>
>> ---
>> fs/xfs/xfs_iomap.c | 33 +++++++++++++++++++++++++++++++--
>> 1 file changed, 31 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
>> index e552ce541ec2..80b6c48e88af 100644
>> --- a/fs/xfs/xfs_iomap.c
>> +++ b/fs/xfs/xfs_iomap.c
>> @@ -881,18 +881,28 @@ xfs_buffered_write_iomap_begin(
>> bool eof = false, cow_eof = false, shared = false;
>> int allocfork = XFS_DATA_FORK;
>> int error = 0;
>> + bool no_wait = (flags & IOMAP_NOWAIT);
>>
>> if (xfs_is_shutdown(mp))
>> return -EIO;
>>
>> /* we can't use delayed allocations when using extent size hints */
>> - if (xfs_get_extsz_hint(ip))
>> + if (xfs_get_extsz_hint(ip)) {
>> + if (no_wait)
>> + return -EAGAIN;
>> +
>> return xfs_direct_write_iomap_begin(inode, offset, count,
>> flags, iomap, srcmap);
>
> Why can't we do IOMAP_NOWAIT allocation here?
> xfs_direct_write_iomap_begin() supports IOMAP_NOWAIT semantics just
> fine - that's what the direct IO path uses...
I'll make that change in the next version.
>
>> + }
>>
>> ASSERT(!XFS_IS_REALTIME_INODE(ip));
>>
>> - xfs_ilock(ip, XFS_ILOCK_EXCL);
>> + if (no_wait) {
>> + if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL))
>> + return -EAGAIN;
>> + } else {
>> + xfs_ilock(ip, XFS_ILOCK_EXCL);
>> + }
>
> handled by xfs_ilock_for_iomap().
The helper xfs_ilock_for_iomap cannot be used for this purpose. The function
xfs_ilock_for_iomap tries to deduce the lock mode. For the function xfs_file_buffered_write()
the lock mode must be exclusive. However this is not always the case when the
helper xfs_ilock_for_iomap is used. There are cases where xfs_is_cow_inode(() is not
true.
I'll add a new helper that will be used here.
>>
>> if (XFS_IS_CORRUPT(mp, !xfs_ifork_has_extents(&ip->i_df)) ||
>> XFS_TEST_ERROR(false, mp, XFS_ERRTAG_BMAPIFORMAT)) {
>> @@ -902,6 +912,11 @@ xfs_buffered_write_iomap_begin(
>>
>> XFS_STATS_INC(mp, xs_blk_mapw);
>>
>> + if (no_wait && xfs_need_iread_extents(XFS_IFORK_PTR(ip, XFS_DATA_FORK))) {
>> + error = -EAGAIN;
>> + goto out_unlock;
>> + }
>> +
>
> Also handled by xfs_ilock_for_iomap().
I'll remove this check with the next version.
>
>> error = xfs_iread_extents(NULL, ip, XFS_DATA_FORK);
>> if (error)
>> goto out_unlock;
>> @@ -933,6 +948,10 @@ xfs_buffered_write_iomap_begin(
>> if (xfs_is_cow_inode(ip)) {
>> if (!ip->i_cowfp) {
>> ASSERT(!xfs_is_reflink_inode(ip));
>> + if (no_wait) {
>> + error = -EAGAIN;
>> + goto out_unlock;
>> + }
>> xfs_ifork_init_cow(ip);
>> }
>
> Also handled by xfs_ilock_for_iomap().
>
I'll remove this check with the next version.
>> cow_eof = !xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb,
>> @@ -956,6 +975,11 @@ xfs_buffered_write_iomap_begin(
>> goto found_imap;
>> }
>>
>> + if (no_wait) {
>> + error = -EAGAIN;
>> + goto out_unlock;
>> + }
>> +
>
> Won't get here because this is COW path, and xfs_ilock_for_iomap()
> handles returning -EAGAIN for that case.
I'll remove this check with the next version.
>
>> xfs_trim_extent(&imap, offset_fsb, end_fsb - offset_fsb);
>>
>> /* Trim the mapping to the nearest shared extent boundary. */
>> @@ -993,6 +1017,11 @@ xfs_buffered_write_iomap_begin(
>> allocfork = XFS_COW_FORK;
>> }
>>
>> + if (no_wait) {
>> + error = -EAGAIN;
>> + goto out_unlock;
>> + }
>
> Why? Delayed allocation doesn't block...
I'll remove this check with the next version.
>
> Cheers,
>
> Dave.
>
