| Message ID | 20190909182722.16783-13-hch@lst.de (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [01/19] iomap: better document the IOMAP_F_* flags | expand |
On Mon, Sep 09, 2019 at 08:27:15PM +0200, Christoph Hellwig wrote: > Replace our local hacks to report the source block in the main iomap > with the proper scrmap reporting. > > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > fs/xfs/xfs_iomap.c | 49 +++++++++++++++++++++++----------------------- > 1 file changed, 24 insertions(+), 25 deletions(-) > > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c > index 18a0f8a5d8c9..d12eacdc9bba 100644 > --- a/fs/xfs/xfs_iomap.c > +++ b/fs/xfs/xfs_iomap.c > @@ -527,7 +527,8 @@ xfs_file_iomap_begin_delay( > loff_t offset, > loff_t count, > unsigned flags, > - struct iomap *iomap) > + struct iomap *iomap, > + struct iomap *srcmap) > { > struct xfs_inode *ip = XFS_I(inode); > struct xfs_mount *mp = ip->i_mount; > @@ -721,11 +722,13 @@ xfs_file_iomap_begin_delay( > found_cow: > xfs_iunlock(ip, XFS_ILOCK_EXCL); > if (imap.br_startoff <= offset_fsb) { > - /* ensure we only report blocks we have a reservation for */ > - xfs_trim_extent(&imap, cmap.br_startoff, cmap.br_blockcount); > - return xfs_bmbt_to_iomap(ip, iomap, &imap, IOMAP_F_SHARED); > + error = xfs_bmbt_to_iomap(ip, srcmap, &imap, 0); > + if (error) > + return error; > + } else { > + xfs_trim_extent(&cmap, offset_fsb, > + imap.br_startoff - offset_fsb); > } > - xfs_trim_extent(&cmap, offset_fsb, imap.br_startoff - offset_fsb); > return xfs_bmbt_to_iomap(ip, iomap, &cmap, IOMAP_F_SHARED); > > out_unlock: > @@ -933,7 +936,7 @@ xfs_file_iomap_begin( > { > struct xfs_inode *ip = XFS_I(inode); > struct xfs_mount *mp = ip->i_mount; > - struct xfs_bmbt_irec imap; > + struct xfs_bmbt_irec imap, cmap; > xfs_fileoff_t offset_fsb, end_fsb; > int nimaps = 1, error = 0; > bool shared = false; > @@ -947,7 +950,7 @@ xfs_file_iomap_begin( > !IS_DAX(inode) && !xfs_get_extsz_hint(ip)) { > /* Reserve delalloc blocks for regular writeback. */ > return xfs_file_iomap_begin_delay(inode, offset, length, flags, > - iomap); > + iomap, srcmap); > } > > /* > @@ -987,9 +990,6 @@ xfs_file_iomap_begin( > * been done up front, so we don't need to do them here. > */ > if (xfs_is_cow_inode(ip)) { > - struct xfs_bmbt_irec cmap; > - bool directio = (flags & IOMAP_DIRECT); > - > /* if zeroing doesn't need COW allocation, then we are done. */ > if ((flags & IOMAP_ZERO) && > !needs_cow_for_zeroing(&imap, nimaps)) > @@ -997,23 +997,11 @@ xfs_file_iomap_begin( > > /* may drop and re-acquire the ilock */ > error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared, > - &lockmode, directio); > + &lockmode, flags & IOMAP_DIRECT); > if (error) > goto out_unlock; > - > - /* > - * For buffered writes we need to report the address of the > - * previous block (if there was any) so that the higher level > - * write code can perform read-modify-write operations; we > - * won't need the CoW fork mapping until writeback. For direct > - * I/O, which must be block aligned, we need to report the > - * newly allocated address. If the data fork has a hole, copy > - * the COW fork mapping to avoid allocating to the data fork. > - */ > - if (shared && > - (directio || imap.br_startblock == HOLESTARTBLOCK)) > - imap = cmap; > - > + if (shared) > + goto out_found_cow; > end_fsb = imap.br_startoff + imap.br_blockcount; > length = XFS_FSB_TO_B(mp, end_fsb) - offset; > } > @@ -1067,6 +1055,17 @@ xfs_file_iomap_begin( > trace_xfs_iomap_found(ip, offset, length, XFS_DATA_FORK, &imap); > goto out_finish; > > +out_found_cow: > + xfs_iunlock(ip, lockmode); > + length = XFS_FSB_TO_B(mp, cmap.br_startoff + cmap.br_blockcount); > + trace_xfs_iomap_found(ip, offset, length - offset, XFS_COW_FORK, &cmap); > + if (imap.br_startblock != HOLESTARTBLOCK) { TBH I've been wondering for a while now if it would make more sense to do this in iomap_apply (and the open-coded versions in dax.c): struct iomap srcmap = { .type = IOMAP_HOLE }; in the iomap_apply function (and change the "if (!srcmap.type)" checks to "if (srcmap.type != IOMAP_HOLE)"). That would get rid of the weird situation where iomap.h doesn't define an iomap type name corresponding to 0 but clearly it has some special meaning because the iomap code changes behavior based on that. It also strikes me as weird that for the @imap parameter, type == 0 would be considered a coding error but for @srcmap, we use type == 0 to mean "no mapping" but we don't do that for @srcmap.type == IOMAP_HOLE. I mention that because, if some ->iomap_begin function returns IOMAP_HOLE then iomap_apply will pass the (hole) srcmap as the second parameter to the ->actor function. When that happens, iomap_write_begin call will try to fill in the rest of the page from @srcmap (which is hole), not the @iomap (which might not be a hole) which seems wrong. As for this function, if we made the above change, then the conditional becomes unneccessary -- we know this is a COW write, so we call xfs_bmbt_to_iomap on both mappings and exit. No need for special casing. --D > + error = xfs_bmbt_to_iomap(ip, srcmap, &imap, 0); > + if (error) > + return error; > + } > + return xfs_bmbt_to_iomap(ip, iomap, &cmap, IOMAP_F_SHARED); > + > out_unlock: > xfs_iunlock(ip, lockmode); > return error; > -- > 2.20.1 >
On Wed, Sep 18, 2019 at 10:52:28AM -0700, Darrick J. Wong wrote: > TBH I've been wondering for a while now if it would make more sense to > do this in iomap_apply (and the open-coded versions in dax.c): > > struct iomap srcmap = { .type = IOMAP_HOLE }; > > in the iomap_apply function (and change the "if (!srcmap.type)" checks > to "if (srcmap.type != IOMAP_HOLE)"). That would get rid of the weird > situation where iomap.h doesn't define an iomap type name corresponding > to 0 but clearly it has some special meaning because the iomap code > changes behavior based on that. > > It also strikes me as weird that for the @imap parameter, type == 0 > would be considered a coding error but for @srcmap, we use type == 0 to > mean "no mapping" but we don't do that for @srcmap.type == IOMAP_HOLE. > > I mention that because, if some ->iomap_begin function returns > IOMAP_HOLE then iomap_apply will pass the (hole) srcmap as the second > parameter to the ->actor function. When that happens, iomap_write_begin > call will try to fill in the rest of the page from @srcmap (which is > hole), not the @iomap (which might not be a hole) which seems wrong. I've renumber IOMAP_HOLE and initialized all the maps to it, that seems like a nice improvement. > As for this function, if we made the above change, then the conditional > becomes unneccessary -- we know this is a COW write, so we call > xfs_bmbt_to_iomap on both mappings and exit. No need for special > casing. OTOH I can't really agree to this. We now do pointless extra work for a common case, which also seems a little confusing. It also goes again the future direction where at least for some cases I want to avoid the imap lookup entirely if we don't need it.
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c index 18a0f8a5d8c9..d12eacdc9bba 100644 --- a/fs/xfs/xfs_iomap.c +++ b/fs/xfs/xfs_iomap.c @@ -527,7 +527,8 @@ xfs_file_iomap_begin_delay( loff_t offset, loff_t count, unsigned flags, - struct iomap *iomap) + struct iomap *iomap, + struct iomap *srcmap) { struct xfs_inode *ip = XFS_I(inode); struct xfs_mount *mp = ip->i_mount; @@ -721,11 +722,13 @@ xfs_file_iomap_begin_delay( found_cow: xfs_iunlock(ip, XFS_ILOCK_EXCL); if (imap.br_startoff <= offset_fsb) { - /* ensure we only report blocks we have a reservation for */ - xfs_trim_extent(&imap, cmap.br_startoff, cmap.br_blockcount); - return xfs_bmbt_to_iomap(ip, iomap, &imap, IOMAP_F_SHARED); + error = xfs_bmbt_to_iomap(ip, srcmap, &imap, 0); + if (error) + return error; + } else { + xfs_trim_extent(&cmap, offset_fsb, + imap.br_startoff - offset_fsb); } - xfs_trim_extent(&cmap, offset_fsb, imap.br_startoff - offset_fsb); return xfs_bmbt_to_iomap(ip, iomap, &cmap, IOMAP_F_SHARED); out_unlock: @@ -933,7 +936,7 @@ xfs_file_iomap_begin( { struct xfs_inode *ip = XFS_I(inode); struct xfs_mount *mp = ip->i_mount; - struct xfs_bmbt_irec imap; + struct xfs_bmbt_irec imap, cmap; xfs_fileoff_t offset_fsb, end_fsb; int nimaps = 1, error = 0; bool shared = false; @@ -947,7 +950,7 @@ xfs_file_iomap_begin( !IS_DAX(inode) && !xfs_get_extsz_hint(ip)) { /* Reserve delalloc blocks for regular writeback. */ return xfs_file_iomap_begin_delay(inode, offset, length, flags, - iomap); + iomap, srcmap); } /* @@ -987,9 +990,6 @@ xfs_file_iomap_begin( * been done up front, so we don't need to do them here. */ if (xfs_is_cow_inode(ip)) { - struct xfs_bmbt_irec cmap; - bool directio = (flags & IOMAP_DIRECT); - /* if zeroing doesn't need COW allocation, then we are done. */ if ((flags & IOMAP_ZERO) && !needs_cow_for_zeroing(&imap, nimaps)) @@ -997,23 +997,11 @@ xfs_file_iomap_begin( /* may drop and re-acquire the ilock */ error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared, - &lockmode, directio); + &lockmode, flags & IOMAP_DIRECT); if (error) goto out_unlock; - - /* - * For buffered writes we need to report the address of the - * previous block (if there was any) so that the higher level - * write code can perform read-modify-write operations; we - * won't need the CoW fork mapping until writeback. For direct - * I/O, which must be block aligned, we need to report the - * newly allocated address. If the data fork has a hole, copy - * the COW fork mapping to avoid allocating to the data fork. - */ - if (shared && - (directio || imap.br_startblock == HOLESTARTBLOCK)) - imap = cmap; - + if (shared) + goto out_found_cow; end_fsb = imap.br_startoff + imap.br_blockcount; length = XFS_FSB_TO_B(mp, end_fsb) - offset; } @@ -1067,6 +1055,17 @@ xfs_file_iomap_begin( trace_xfs_iomap_found(ip, offset, length, XFS_DATA_FORK, &imap); goto out_finish; +out_found_cow: + xfs_iunlock(ip, lockmode); + length = XFS_FSB_TO_B(mp, cmap.br_startoff + cmap.br_blockcount); + trace_xfs_iomap_found(ip, offset, length - offset, XFS_COW_FORK, &cmap); + if (imap.br_startblock != HOLESTARTBLOCK) { + error = xfs_bmbt_to_iomap(ip, srcmap, &imap, 0); + if (error) + return error; + } + return xfs_bmbt_to_iomap(ip, iomap, &cmap, IOMAP_F_SHARED); + out_unlock: xfs_iunlock(ip, lockmode); return error;
Replace our local hacks to report the source block in the main iomap with the proper scrmap reporting. Signed-off-by: Christoph Hellwig <hch@lst.de> --- fs/xfs/xfs_iomap.c | 49 +++++++++++++++++++++++----------------------- 1 file changed, 24 insertions(+), 25 deletions(-)