Re: FIDEDUPERANGE woes

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2019/12/13 上午12:15, halfdog wrote:
> Hello list,
> 
> Using btrfs on
> 
> Linux version 5.3.0-2-amd64 (debian-kernel@lists.debian.org) (gcc version 9.2.1 20191109 (Debian 9.2.1-19)) #1 SMP Debian 5.3.9-3 (2019-11-19)
> 
> the FIDEDUPERANGE exposes weird behaviour on two identical but
> not too large files that seems to be depending on the file size.
> Before FIDEDUPERANGE both files have a single extent, afterwards
> first file is still single extent, second file has all bytes sharing
> with the extent of the first file except for the last 4096 bytes.
> 
> Is there anything known about a bug fixed since the above mentioned
> kernel version?
> 
> 
> 
> If no, does following reproducer still show the same behaviour
> on current Linux kernel (my Python test tools also attached)?
> 
>> dd if=/dev/zero bs=1M count=32 of=disk
>> mkfs.btrfs --mixed --metadata single --data single --nodesize 4096 disk
>> mount disk /mnt/test
>> mkdir /mnt/test/x
>> dd bs=1 count=155489 if=/dev/urandom of=/mnt/test/x/file-0

155489 is not sector size aligned, thus the last extent will be padded
with zero.

>> cat /mnt/test/x/file-0 > /mnt/test/x/file-1

Same for the new file.

For the tailing padding part, it's not aligned, and it's smaller than
the inode size.

Thus we won't dedupe that tailing part.

Thanks,
Qu

> 
>> ./SimpleIndexer x > x.json
>> ./IndexDeduplicationAnalyzer --IndexFile /mnt/test/x.json /mnt/test/x > dedup.list
> Got dict: {b'/mnt/test/x/file-0': [(0, 5316608, 155648)], b'/mnt/test/x/file-1': [(0, 5472256, 155648)]}
> ...
>> strace -s256 -f btrfs-extent-same 155489 /mnt/test/x/file-0 0 /mnt/test/x/file-1 0 2>&1 | grep -E -e FIDEDUPERANGE
> ioctl(3, BTRFS_IOC_FILE_EXTENT_SAME or FIDEDUPERANGE, {src_offset=0, src_length=155489, dest_count=1, info=[{dest_fd=4, dest_offset=0}]} => {info=[{bytes_deduped=155489, status=0}]}) = 0
>> ./IndexDeduplicationAnalyzer --IndexFile /mnt/test/x.json /mnt/test/x > dedup.list
> Got dict: {b'/mnt/test/x/file-0': [(0, 5316608, 155648)], b'/mnt/test/x/file-1': [(0, 5316608, 151552), (151552, 5623808, 4096)]}
> ...
>> strace -s256 -f btrfs-extent-same 155489 /mnt/test/x/file-0 0 /mnt/test/x/file-1 0 2>&1 | grep -E -e FIDEDUPERANGE
> ioctl(3, BTRFS_IOC_FILE_EXTENT_SAME or FIDEDUPERANGE, {src_offset=0, src_length=155489, dest_count=1, info=[{dest_fd=4, dest_offset=0}]} => {info=[{bytes_deduped=155489, status=0}]}) = 0
>> strace -s256 -f btrfs-extent-same 4096 /mnt/test/x/file-0 151552 /mnt/test/x/file-1 151552 2>&1 | grep -E -e FIDEDUPERANGE
> ioctl(3, BTRFS_IOC_FILE_EXTENT_SAME or FIDEDUPERANGE, {src_offset=151552, src_length=4096, dest_count=1, info=[{dest_fd=4, dest_offset=151552}]}) = -1 EINVAL (Invalid argument)
> 


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