zcat: failure to correctly extract files

[Jack Mitchell]

On 15/06/14 22:47, Denys Vlasenko wrote:
> On Friday 13 June 2014 11:28, Jack Mitchell wrote:
>> I have recently upgraded to busybox v1.18.3 to v1.22.1 and seem to have
>> discovered a bug in zcat.
>>
>> I'm not entirely sure what the problem is, but files don't seem to be
>> extracted correctly. The following procedure creates a basic filesytem
>> image, gzips it on the host then scp's it to the target where zcat fails
>> to properly extract it, while gunzip -c succeeds. It's very similar to
>> my use-case and shows the issue.
>>
>> On the host:
>>
>> [jack at jackArch busybox-test]$ dd if=/dev/zero of=test.img bs=1MB count=100
>> 100+0 records in
>> 100+0 records out
>> 100000000 bytes (100 MB) copied, 0.157787 s, 634 MB/s
>>
>> [jack at jackArch busybox-test]$ mkfs.ext3 test.img
>> mke2fs 1.42.9 (28-Dec-2013)
>> Allocating group tables: done
>> Writing inode tables: done
>> Creating journal (4096 blocks): done
>> Writing superblocks and filesystem accounting information: done
>>
>> [jack at jackArch busybox-test]$ sudo mount test.img /mnt/tmp
>> [sudo] password for jack:
>>
>> [jack at jackArch busybox-test]$ ls -la /mnt/tmp
>> total 17
>> drwxr-xr-x  3 root root  1024 Jun 12 17:14 .
>> drwxr-xr-x 10 root root  4096 Jun  9 13:18 ..
>> drwx------  2 root root 12288 Jun 12 17:14 lost+found
>>
>> [jack at jackArch busybox-test]$ sudo umount /mnt/tmp
>>
>> [jack at jackArch busybox-test]$ dd if=test.img bs=1k | gzip -v9 > test-zcat
>> 97656+1 records in
>> 97656+1 records out
>> 100000000 bytes (100 MB) copied, 0.574901 s, 174 MB/s
>>  99.9%
>>
>> [jack at jackArch busybox-test]$ scp test-zcat root at 192.168.0.254:/mnt/persist
>> test-zcat
>> 100%  108KB 108.5KB/s   00:00
>>
>>
>> On the target:
>>
>> target# pwd
>> /mnt/persist
>>
>> target# ls -lah test-zcat
>> -rw-r--r--    1 root     root      108.5K Jun 13 09:19 test-zcat
>>
>> target# time zcat test-zcat > test.img
>> real	0m 0.00s
>> user	0m 0.00s
>> sys	0m 0.00s
>>
>> target# ls -lah test.img
>> -rw-r--r--    1 root     root      108.5K Jun 13 09:20 test.img
>>
>> target# mount test.img /mnt/tmp/
>> mount: wrong fs type, bad option, bad superblock on /dev/loop4,
>>        missing codepage or helper program, or other error
>>
>>        In some cases useful info is found in syslog - try
>>        dmesg | tail or so.
>>
>> target# time gunzip -c test-zcat > test2.img
>> real	0m 1.90s
>> user	0m 1.31s
>> sys	0m 0.58s
>>
>> target# ls -lah test2.img
>> -rw-r--r--    1 root     root       95.4M Jun 13 09:21 test2.img
>>
>> target# mount test2.img /mnt/tmp/
>>
>> target# ls -la /mnt/tmp/
>> drwxr-xr-x    3 root     root          1024 Jun 12 16:14 .
>> drwxr-xr-x    9 root     root          4096 Jun 12 16:32 ..
>> drwx------    2 root     root         12288 Jun 12 16:14 lost+found
>>
>> If you have any questions please let me know and I'll do my best to help.
> 
> 
> Please try current git. I remember there was a fix for this.
> 

Hi Denys,

Correct, zcat works as expected at the current git HEAD.

Cheers,
Jack.

-- 
  Jack Mitchell (jack at embed.me.uk)
  Embedded Systems Engineer
  Cambridgeshire, UK
  http://www.embed.me.uk
--