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Message-ID: <alpine.LFD.2.00.1405061736390.2255@localhost.localdomain> Date: Tue, 6 May 2014 17:45:01 +0200 (CEST) From: Lukáš Czerner <lczerner@...hat.com> To: "Darrick J. Wong" <darrick.wong@...cle.com> cc: tytso@....edu, linux-ext4@...r.kernel.org Subject: Re: [PATCH 16/37] libext2fs: support allocating uninit blocks in bmap2() On Thu, 1 May 2014, Darrick J. Wong wrote: > Date: Thu, 01 May 2014 16:14:07 -0700 > From: Darrick J. Wong <darrick.wong@...cle.com> > To: tytso@....edu, darrick.wong@...cle.com > Cc: linux-ext4@...r.kernel.org > Subject: [PATCH 16/37] libext2fs: support allocating uninit blocks in bmap2() > > In order to support fallocate, we need to be able to have > ext2fs_bmap2() allocate blocks and put them into uninitialized > extents. There's a flag to do this in the extent code, but it's not > exposed to the bmap2 interface, so plumb that in. Eventually fuse2fs > or somebody will use it. > > Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com> > --- > lib/ext2fs/bmap.c | 24 ++++++++++++++++++++++-- > lib/ext2fs/ext2fs.h | 1 + > lib/ext2fs/mkjournal.c | 17 +++++++++++++++++ > 3 files changed, 40 insertions(+), 2 deletions(-) > > > diff --git a/lib/ext2fs/bmap.c b/lib/ext2fs/bmap.c > index c1d0e6f..a4dc8ef 100644 > --- a/lib/ext2fs/bmap.c > +++ b/lib/ext2fs/bmap.c > @@ -72,6 +72,11 @@ static _BMAP_INLINE_ errcode_t block_ind_bmap(ext2_filsys fs, int flags, > block_buf + fs->blocksize, &b); > if (retval) > return retval; > + if (flags & BMAP_UNINIT) { > + retval = ext2fs_zero_blocks2(fs, b, 1, NULL, NULL); > + if (retval) > + return retval; > + } > > #ifdef WORDS_BIGENDIAN > ((blk_t *) block_buf)[nr] = ext2fs_swab32(b); > @@ -214,10 +219,13 @@ static errcode_t extent_bmap(ext2_filsys fs, ext2_ino_t ino, > errcode_t retval = 0; > blk64_t blk64 = 0; > int alloc = 0; > + int set_flags; > + > + set_flags = bmap_flags & BMAP_UNINIT ? EXT2_EXTENT_SET_BMAP_UNINIT : 0; > > if (bmap_flags & BMAP_SET) { > retval = ext2fs_extent_set_bmap(handle, block, > - *phys_blk, 0); > + *phys_blk, set_flags); > return retval; > } > retval = ext2fs_extent_goto(handle, block); > @@ -254,7 +262,7 @@ got_block: > alloc++; > set_extent: > retval = ext2fs_extent_set_bmap(handle, block, > - blk64, 0); > + blk64, set_flags); > if (retval) { > ext2fs_block_alloc_stats2(fs, blk64, -1); > return retval; > @@ -345,6 +353,12 @@ errcode_t ext2fs_bmap2(ext2_filsys fs, ext2_ino_t ino, struct ext2_inode *inode, > goto done; > } > > + if ((bmap_flags & BMAP_SET) && (bmap_flags & BMAP_UNINIT)) { > + retval = ext2fs_zero_blocks2(fs, *phys_blk, 1, NULL, NULL); > + if (retval) > + goto done; > + } > + > if (block < EXT2_NDIR_BLOCKS) { > if (bmap_flags & BMAP_SET) { > b = *phys_blk; > @@ -360,6 +374,12 @@ errcode_t ext2fs_bmap2(ext2_filsys fs, ext2_ino_t ino, struct ext2_inode *inode, > retval = ext2fs_alloc_block(fs, b, block_buf, &b); > if (retval) > goto done; > + if (bmap_flags & BMAP_UNINIT) { > + retval = ext2fs_zero_blocks2(fs, b, 1, NULL, > + NULL); > + if (retval) > + goto done; > + } > inode_bmap(inode, block) = b; > blocks_alloc++; > *phys_blk = b; > diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h > index 599c972..819a14a 100644 > --- a/lib/ext2fs/ext2fs.h > +++ b/lib/ext2fs/ext2fs.h > @@ -527,6 +527,7 @@ typedef struct ext2_icount *ext2_icount_t; > */ > #define BMAP_ALLOC 0x0001 > #define BMAP_SET 0x0002 > +#define BMAP_UNINIT 0x0004 > > /* > * Returned flags from ext2fs_bmap > diff --git a/lib/ext2fs/mkjournal.c b/lib/ext2fs/mkjournal.c > index 884d9c0..ecc3912 100644 > --- a/lib/ext2fs/mkjournal.c > +++ b/lib/ext2fs/mkjournal.c > @@ -174,6 +174,23 @@ errcode_t ext2fs_zero_blocks2(ext2_filsys fs, blk64_t blk, int num, > return ENOMEM; > memset(buf, 0, fs->blocksize * STRIDE_LENGTH); > } > + > + /* Try discard, if it zeroes data... */ > + if (io_channel_discard_zeroes_data(fs->io)) { > + memset(buf + fs->blocksize, 0, fs->blocksize); > + retval = io_channel_discard(fs->io, blk, num); > + if (retval) > + goto skip_discard; > + retval = io_channel_read_blk64(fs->io, blk, 1, buf); > + if (retval) > + goto skip_discard; > + if (memcmp(buf, buf + fs->blocksize, fs->blocksize) == 0) > + return 0; > + /* Hah! Discard doesn't zero! */ > + fs->io->flags &= ~CHANNEL_FLAGS_DISCARD_ZEROES; > + } > +skip_discard: You did not mention that in the description, but this is actually a problem. The reason is that discard might not be reliable on some devices. This has been discussed several times and I am not the only one who've seen that even if the device itself says that it will return zeroes from discarded regions sometimes it might return data. I would rather avoid this kind of optimization. However if the underlying "device" is a loop device then it will be reliable if it's supported. Also if then underlying "device" is a image then we can just simply use punch hole. Thanks! -Lukas > + > /* OK, do the write loop */ > j=0; > while (j < num) { > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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