On 2/23/11 9:59 AM, Yongqiang Yang wrote: > 1] Delayed extents after a hole are neglected. > > By using find_get_pages() instead of find_get_page() to > lookup pagecache, delayed extents can be found, because > find_get_pages() with nr_pages=1 will return the next page > in pagecache. > > 2] Extents after a delayed extent or a hole are neglected as well. > > Fix it by accurating the request range by the result of > ext4_ext_next_allocated_block(). > > Reported by Chris Mason <chris.mason@xxxxxxxxxx>: > We've had reports on btrfs that cp is giving us files full of zeros > instead of actually copying them. It was tracked down to a bug with > the btrfs fiemap implementation where it was returning holes for > delalloc ranges. > > Newer versions of cp are trusting fiemap to tell it where the holes > are, which does seem like a pretty neat trick. > > I decided to give xfs and ext4 a shot with a few tests cases too, xfs > passed with all the ones btrfs was getting wrong, and ext4 got the basic > delalloc case right. > $ mkfs.ext4 /dev/xxx > $ mount /dev/xxx /mnt > $ dd if=/dev/zero of=/mnt/foo bs=1M count=1 > $ fiemap-test foo > ext: 0 logical: [ 0.. 255] phys: 0.. 255 > flags: 0x007 tot: 256 > > Horray! But once we throw a hole in, things go bad: > $ mkfs.ext4 /dev/xxx > $ mount /dev/xxx /mnt > $ dd if=/dev/zero of=/mnt/foo bs=1M count=1 seek=1 > $ fiemap-test foo > < no output > > > We've got a delalloc extent after the hole and ext4 fiemap didn't find > it. If I run sync to kick the delalloc out: > $sync > $ fiemap-test foo > ext: 0 logical: [ 256.. 511] phys: 34048.. 34303 > flags: 0x001 tot: 256 > > fiemap-test is sitting in my /usr/local/bin, and I have no idea how it > got there. It's full of pretty comments so I know it isn't mine, but > you can grab it here: > > http://oss.oracle.com/~mason/fiemap-test.c > > xfsqa has a fiemap program too. > > After Fix, test results are as follows: > ext: 0 logical: [ 256.. 511] phys: 0.. 255 > flags: 0x007 tot: 256 > ext: 0 logical: [ 256.. 511] phys: 33280.. 33535 > flags: 0x001 tot: 256 > > Signe-off-by: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx> > --- > fs/ext4/extents.c | 26 +++++++++++++++++++++++--- > mm/filemap.c | 1 + > 2 files changed, 24 insertions(+), 3 deletions(-) > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c > index ccce8a7..ad455a0 100644 > --- a/fs/ext4/extents.c > +++ b/fs/ext4/extents.c > @@ -3788,17 +3788,27 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path, > __u64 physical; > __u64 length; > __u32 flags = 0; > + ext4_lblk_t end; > int error; > > logical = (__u64)newex->ec_block << blksize_bits; > > - if (newex->ec_start == 0) { > + if (!newex->ec_start) { > + /* > + * There is no extent contains @newex->ec_block block. > + * It implies that @newex->ec_block block lies 1)a hole > + * or 2)delayed-allocated blocks that has not been > + * allocated, so pagecache is needed to lookup. > + * > + * And if it is case 2, @newex->ec_len needs to be corrected. > + * > + */ > pgoff_t offset; > struct page *page; > struct buffer_head *bh = NULL; > > offset = logical >> PAGE_SHIFT; > - page = find_get_page(inode->i_mapping, offset); > + (void)find_get_pages(inode->i_mapping, offset, 1, &page); > if (!page || !page_has_buffers(page)) > return EXT_CONTINUE; > > @@ -3807,8 +3817,13 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path, > if (!bh) > return EXT_CONTINUE; > > + /* Assume block-size equals page-size. */ > if (buffer_delay(bh)) { > flags |= FIEMAP_EXTENT_DELALLOC; > + if (page->index > offset) { > + logical = ((__u64)page->index << PAGE_SHIFT); > + newex->ec_block = logical >> blksize_bits; > + } > page_cache_release(page); > } else { > page_cache_release(page); > @@ -3830,7 +3845,8 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path, > * > * XXX this might miss a single-block extent at EXT_MAX_BLOCK > */ > - if (ext4_ext_next_allocated_block(path) == EXT_MAX_BLOCK || > + end = ext4_ext_next_allocated_block(path); I think this will fall down if you have: [ HOLE ][ DELALLOC ][ HOLE ][ ALLOCATED ] won't it? i.e. your "end" will be the first block of "allocated" right? -Eric > + if (end == EXT_MAX_BLOCK || > newex->ec_block + newex->ec_len - 1 == EXT_MAX_BLOCK) { > loff_t size = i_size_read(inode); > loff_t bs = EXT4_BLOCK_SIZE(inode->i_sb); > @@ -3839,8 +3855,12 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path, > if ((flags & FIEMAP_EXTENT_DELALLOC) && > logical+length > size) > length = (size - logical + bs - 1) & ~(bs-1); > + } else { > + newex->ec_len = end - newex->ec_block; > + length = (__u64)newex->ec_len << blksize_bits; > } > > + > error = fiemap_fill_next_extent(fieinfo, logical, physical, > length, flags); > if (error < 0) > diff --git a/mm/filemap.c b/mm/filemap.c > index 83a45d3..1c01ffc 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -803,6 +803,7 @@ repeat: > rcu_read_unlock(); > return ret; > } > +EXPORT_SYMBOL(find_get_pages); > > /** > * find_get_pages_contig - gang contiguous pagecache lookup -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
