Am Thu, 21 Dec 2017 13:51:40 -0500 schrieb Chris Mason:
> On 12/20/2017 03:59 PM, Timofey Titovets wrote:
>> How reproduce:
>> touch test_file
>> chattr +C test_file
>> dd if=/dev/zero of=test_file bs=1M count=1
>> btrfs fi def -vrczlib test_file
>> filefrag -v test_file
>>
>> test_file
>> Filesystem type is: 9123683e
>> File size of test_file is 1048576 (256 blocks of 4096 bytes)
>> ext: logical_offset:physical_offset: length: expected: flags:
>>0:0.. 31: 72917050.. 72917081: 32: encoded
>>1: 32.. 63: 72917118.. 72917149: 32: 72917082: encoded
>>2: 64.. 95: 72919494.. 72919525: 32: 72917150: encoded
>>3: 96.. 127: 72927576.. 72927607: 32: 72919526: encoded
>>4: 128.. 159: 72943261.. 72943292: 32: 72927608: encoded
>>5: 160.. 191: 72944929.. 72944960: 32: 72943293: encoded
>>6: 192.. 223: 72944952.. 72944983: 32: 72944961: encoded
>>7: 224.. 255: 72967084.. 72967115: 32: 72944984:
>> last,encoded,eof
>> test_file: 8 extents found
>>
>> I can't found at now, where that error happen in code,
>> but it's reproducible on Linux 4.14.8
>
> We'll silently cow in a few cases, this is one.
I think the question was about compression, not cow.
I can reproduce this behavior:
$ touch nocow.dat
$ touch cow.dat
$ chattr +c cow.dat
$ chattr +C nocow.dat
$ dd if=/dev/zero of=cow.dat count=1 bs=1M
$ dd if=/dev/zero of=nocow.dat count=1 bs=1M
$ filefrag -v cow.dat
Filesystem type is: 9123683e
File size of cow.dat is 1048576 (256 blocks of 4096 bytes)
ext: logical_offset:physical_offset: length: expected: flags:
0:0.. 31: 1044845154..1044845185: 32:
encoded,shared
1: 32.. 63: 1044845166..1044845197: 32: 1044845186:
encoded,shared
2: 64.. 95: 1044845167..1044845198: 32: 1044845198:
encoded,shared
3: 96.. 127: 1044851064..1044851095: 32: 1044845199:
encoded,shared
4: 128.. 159: 1044851065..1044851096: 32: 1044851096:
encoded,shared
5: 160.. 191: 1044852160..1044852191: 32: 1044851097:
encoded,shared
6: 192.. 223: 1044943106..1044943137: 32: 1044852192:
encoded,shared
7: 224.. 255: 1045054792..1045054823: 32: 1044943138:
last,encoded,shared,eof
cow.dat: 8 extents found
$ filefrag -v nocow.dat
Filesystem type is: 9123683e
File size of nocow.dat is 1048576 (256 blocks of 4096 bytes)
ext: logical_offset:physical_offset: length: expected: flags:
0:0.. 255: 1196077983..1196078238:256:
last,shared,eof
nocow.dat: 1 extent found
Now it seems to be compressed (8x 128k extents):
$ filefrag -v nocow.dat
Filesystem type is: 9123683e
File size of nocow.dat is 1048576 (256 blocks of 4096 bytes)
ext: logical_offset:physical_offset: length: expected: flags:
0:0.. 31: 1121866367..1121866398: 32:
encoded,shared
1: 32.. 63: 1121866369..1121866400: 32: 1121866399:
encoded,shared
2: 64.. 95: 1121866370..1121866401: 32: 1121866401:
encoded,shared
3: 96.. 127: 1121866371..1121866402: 32: 1121866402:
encoded,shared
4: 128.. 159: 1121866372..1121866403: 32: 1121866403:
encoded,shared
5: 160.. 191: 1121866373..1121866404: 32: 1121866404:
encoded,shared
6: 192.. 223: 1121866374..1121866405: 32: 1121866405:
encoded,shared
7: 224.. 255: 1121866375..1121866406: 32: 1121866406:
last,encoded,shared,eof
nocow.dat: 8 extents found
--
Regards,
Kai
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