fiemap is broken for sparse file in ext4?
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From: Tao Ma on 10 Jun 2010 22:20 Hi Ted and other ext4 gurus, I found fiemap may be broken for sparse files in ext4. Here is a simple example. dd if=/dev/zero of=testfile1 bs=1M count=1 using fiemap shows that it has a delalloc extent. Logical: 0 Ext length: 1048576 Physical: 0 flags: 7 flags 7 means FIEMAP_EXTENT_LAST, FIEMAP_EXTENT_UNKNOWN and FIEMAP_EXTENT_DELALLOC, while if we create a sparse file, fiemap will not show the delalloc extent. dd if=/dev/zero of=testfile1 bs=1M count=1 seek=1 using fiemap shows that it has no extent for the file. while we should have some output like: Logical: 1048576 Ext length: 1048576 Physical: 0 flags: 7 So we have different output with sparse and non-sparse file. Is it a bug for ext4? Regards, Tao -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Eric Sandeen on 11 Jun 2010 00:10 Tao Ma wrote: > Hi Ted and other ext4 gurus, > I found fiemap may be broken for sparse files in ext4. Here is a > simple example. > > dd if=/dev/zero of=testfile1 bs=1M count=1 > using fiemap shows that it has a delalloc extent. > Logical: 0 Ext length: 1048576 Physical: 0 flags: 7 > > flags 7 means FIEMAP_EXTENT_LAST, FIEMAP_EXTENT_UNKNOWN and > FIEMAP_EXTENT_DELALLOC, > > while if we create a sparse file, fiemap will not show the delalloc extent. > dd if=/dev/zero of=testfile1 bs=1M count=1 seek=1 > using fiemap shows that it has no extent for the file. while we should > have some output like: > Logical: 1048576 Ext length: 1048576 Physical: 0 flags: 7 > > So we have different output with sparse and non-sparse file. Is it a bug > for ext4? What are you using to call fiemap? Here it seems to be working: # dd if=/dev/zero of=testfile1 bs=1M count=1 seek=1; # filefrag -v testfile1 Filesystem type is: ef53 Filesystem cylinder groups is approximately 119 File size of testfile1 is 2097152 (512 blocks, blocksize 4096) ext logical physical expected length flags 0 256 151946 1 merged 1 257 151951 151946 2 merged 2 259 152434 151952 253 merged,eof testfile1: 4 extents found And with my homegrown fiemap tester: # ./fiemap-test testfile1 ext: 0 logical: [ 256.. 256] phys: 151946.. 151946 flags: 0x1000 tot: 1 ext: 1 logical: [ 257.. 258] phys: 151951.. 151952 flags: 0x1000 tot: 2 ext: 2 logical: [ 259.. 511] phys: 152434.. 152686 flags: 0x1001 tot: 253 .... seems ok here, aside from the fragmentation :) ... -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Tao Ma on 11 Jun 2010 01:10 Hi Eric, Thanks for the quick response. On 06/11/2010 12:08 PM, Eric Sandeen wrote: > Tao Ma wrote: >> Hi Ted and other ext4 gurus, >> I found fiemap may be broken for sparse files in ext4. Here is a >> simple example. >> >> dd if=/dev/zero of=testfile1 bs=1M count=1 >> using fiemap shows that it has a delalloc extent. >> Logical: 0 Ext length: 1048576 Physical: 0 flags: 7 >> >> flags 7 means FIEMAP_EXTENT_LAST, FIEMAP_EXTENT_UNKNOWN and >> FIEMAP_EXTENT_DELALLOC, >> >> while if we create a sparse file, fiemap will not show the delalloc extent. >> dd if=/dev/zero of=testfile1 bs=1M count=1 seek=1 >> using fiemap shows that it has no extent for the file. while we should >> have some output like: >> Logical: 1048576 Ext length: 1048576 Physical: 0 flags: 7 >> >> So we have different output with sparse and non-sparse file. Is it a bug >> for ext4? > > What are you using to call fiemap? Here it seems to be working: I just wrote a simple test program by calling ioctl. It is attached. btw, you need to call it immediately after dd so that we have a chance that ext4 don't have time to allocate extents. ;) > > # dd if=/dev/zero of=testfile1 bs=1M count=1 seek=1; > > # filefrag -v testfile1 > Filesystem type is: ef53 > Filesystem cylinder groups is approximately 119 > File size of testfile1 is 2097152 (512 blocks, blocksize 4096) > ext logical physical expected length flags > 0 256 151946 1 merged > 1 257 151951 151946 2 merged > 2 259 152434 151952 253 merged,eof > testfile1: 4 extents found I guess maybe filefrag use the diffrent ioctl flag, maybe FIEMAP_FLAG_SYNC to let ext4 sync first. Regards, Tao
From: Eric Sandeen on 11 Jun 2010 09:50 Tao Ma wrote: > Hi Eric, > Thanks for the quick response. > > On 06/11/2010 12:08 PM, Eric Sandeen wrote: .... >> What are you using to call fiemap? Here it seems to be working: > I just wrote a simple test program by calling ioctl. It is attached. > btw, you need to call it immediately after dd so that we have a chance > that ext4 don't have time to allocate extents. ;) >> >> # dd if=/dev/zero of=testfile1 bs=1M count=1 seek=1; >> >> # filefrag -v testfile1 >> Filesystem type is: ef53 >> Filesystem cylinder groups is approximately 119 >> File size of testfile1 is 2097152 (512 blocks, blocksize 4096) >> ext logical physical expected length flags >> 0 256 151946 1 merged >> 1 257 151951 151946 2 merged >> 2 259 152434 151952 253 merged,eof >> testfile1: 4 extents found > I guess maybe filefrag use the diffrent ioctl flag, maybe > FIEMAP_FLAG_SYNC to let ext4 sync first. My tester isn't calling sync or using the sync flag, AFAIK. I'll take a look at yours. Thanks, -Eric > Regards, > Tao > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Eric Sandeen on 11 Jun 2010 11:50
Tao Ma wrote: >> What are you using to call fiemap? Here it seems to be working: > I just wrote a simple test program by calling ioctl. It is attached. > btw, you need to call it immediately after dd so that we have a chance > that ext4 don't have time to allocate extents. ;) OK I take it back, I do see it. *cough* too many different filesystems on this box ... ;) Yes, it does look like a bug. -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |