Issue with 'Unknown Error: -512'

[Brandon Falk]

On 7/18/2011 10:18 AM, Andriy Gapon wrote:
> on 18/07/2011 17:53 Brandon Falk said the following:
>> Hello,
>>
>> In recent branches (confirmed with 224119) builds compiled with clang happen to
>> throw 'Unknown error: -512' in a lot of places, making the system unusable.
>> (Untested on gcc compiled systems). Originally I thought the problem was with
>> specific programs, then I narrowed it down to file I/O, and now I've narrowed it
>> down to open() with O_TRUNC. Without O_TRUNC there seems to be no issues
>> whatsoever. With O_TRUNC on open() it fails with that 'Unknown error: -512' every
>> other time you run the program. Common issues, portsnap is affected, making it
>> impossible to fetch/extract ports. As well as redirecting output in shells eg
>> `echo 'hi'>  test` fails every other try. You have the same issue with text
>> editors like `edit` where it fails every other save. There are no issues with
>> `echo 'hi'>>  test` as there is no O_TRUNC, it only seems to be an O_TRUNC error.
>>
>> Any tips? Otherwise I'll be looking into this today myself.
>
> Just a hint that you could try using DTrace syscall and fbt providers to see where
> in kernel (if in kernel) that -512 return value originates.
>

Update:

I've traced more and more into the kernel, and currently I have found 
the following trace:

 >>> ufs_setattr() (in sys/ufs/ufs/ufs_vnops.c:507)
(In truncate a bunch of stuff is done, but it succeeds until VOP_SETATTR)
 >>> vn_truncate() (in sys/kern/vfs_vnops.c:636)
 >>> kern_openat() (in sys/kern/vfs_syscalls.c:1043)
 >>> kern_open()   (in sys/kern/vfs_syscalls.c:1035)
 >>> open() (in sys/kern/vfs_syscalls.c:1006)

ufs_setattr() returns with -1 (EPERM)

I'll continue to try to find the exact problem. A quick workaround 
currently would probably be to use a different filesystem other than 
ufs, but then again, I have no clue if other filesystems have the same 
issue.

Hopefully that trace will help anyone who wants to help out.

-Brandon Falk