iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

xfs: reject all unaligned direct writes to reflinked files

Browse Source 
commit 54a4ef8af4e0dc5c983d17fcb9cf5fd25666d94e upstream.

We currently fall back from direct to buffered writes if we detect a
remaining shared extent in the iomap_begin callback.  But by the time
iomap_begin is called for the potentially unaligned end block we might
have already written most of the data to disk, which we'd now write
again using buffered I/O.  To avoid this reject all writes to reflinked
files before starting I/O so that we are guaranteed to only write the
data once.

The alternative would be to unshare the unaligned start and/or end block
before doing the I/O. I think that's doable, and will actually be
required to support reflinks on DAX file system.  But it will take a
little more time and I'd rather get rid of the double write ASAP.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
[slight changes in context due to the new direct I/O code in 4.10+]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Christoph Hellwig 2017-02-06 13:00:54 -08:00 committed by Greg Kroah-Hartman
parent 67eb7bf836
commit 5bbf5ba693
3 changed files with 10 additions and 46 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
fs/xfs/xfs_aops.c
View File

@ -1263,44 +1263,6 @@ xfs_map_trim_size(
bh_result->b_size = mapping_size;
}
/* Bounce unaligned directio writes to the page cache. */
static int
xfs_bounce_unaligned_dio_write(
struct xfs_inode *ip,
xfs_fileoff_t offset_fsb,
struct xfs_bmbt_irec *imap)
{
struct xfs_bmbt_irec irec;
xfs_fileoff_t delta;
bool shared;
bool x;
int error;
irec = *imap;
if (offset_fsb > irec.br_startoff) {
delta = offset_fsb - irec.br_startoff;
irec.br_blockcount -= delta;
irec.br_startblock += delta;
irec.br_startoff = offset_fsb;
}
error = xfs_reflink_trim_around_shared(ip, &irec, &shared, &x);
if (error)
return error;
/*
* We're here because we're trying to do a directio write to a
* region that isn't aligned to a filesystem block. If any part
* of the extent is shared, fall back to buffered mode to handle
* the RMW. This is done by returning -EREMCHG ("remote addr
* changed"), which is caught further up the call stack.
*/
if (shared) {
trace_xfs_reflink_bounce_dio_write(ip, imap);
return -EREMCHG;
}
return 0;
}
STATIC int
__xfs_get_blocks(
struct inode *inode,
@ -1438,13 +1400,6 @@ __xfs_get_blocks(
if (imap.br_startblock != HOLESTARTBLOCK &&
imap.br_startblock != DELAYSTARTBLOCK &&
(create || !ISUNWRITTEN(&imap))) {
if (create && direct && !is_cow) {
error = xfs_bounce_unaligned_dio_write(ip, offset_fsb,
&imap);
if (error)
return error;
}
xfs_map_buffer(inode, bh_result, &imap, offset);
if (ISUNWRITTEN(&imap))
set_buffer_unwritten(bh_result);

9
fs/xfs/xfs_file.c
View File

@ -554,6 +554,15 @@ xfs_file_dio_aio_write(
if ((iocb->ki_pos & mp->m_blockmask) ||
((iocb->ki_pos + count) & mp->m_blockmask)) {
unaligned_io = 1;
/*
* We can't properly handle unaligned direct I/O to reflink
* files yet, as we can't unshare a partial block.
*/
if (xfs_is_reflink_inode(ip)) {
trace_xfs_reflink_bounce_dio_write(ip, iocb->ki_pos, count);
return -EREMCHG;
}
iolock = XFS_IOLOCK_EXCL;
} else {
iolock = XFS_IOLOCK_SHARED;

2
fs/xfs/xfs_trace.h
View File

@ -3353,7 +3353,7 @@ DEFINE_INODE_IREC_EVENT(xfs_reflink_convert_cow);
DEFINE_RW_EVENT(xfs_reflink_reserve_cow);
DEFINE_RW_EVENT(xfs_reflink_allocate_cow_range);
DEFINE_INODE_IREC_EVENT(xfs_reflink_bounce_dio_write);
DEFINE_SIMPLE_IO_EVENT(xfs_reflink_bounce_dio_write);
DEFINE_IOMAP_EVENT(xfs_reflink_find_cow_mapping);
DEFINE_INODE_IREC_EVENT(xfs_reflink_trim_irec);