On Thu, Feb 24, 2011 at 12:41 AM, Eric Sandeen <sandeen@xxxxxxxxxx> wrote: > 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? We use pagevec_lookup_tag() instead of find_get_page() and check BH_Delay of contiguous pages. Then, we can deal this model. How do you think? > > -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 > > -- Best Wishes Yongqiang Yang -- 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
