errno codes intertwined

errno codes intertwined

[Jan Engelhardt]

Hello lists,


I am currently working on a FUSE-based filesystem much like nfs/sshfs. 
I pass the syscall on to the storage server, where it is executed, and 
get back the result, or errno code. Let's jump into the real world 
example where the storage unit is x86_64 and the mount side is 
sparc/sparc64, and the syscall is getxattr.

If a file does not have the requested attribute, the syscall will 
produce ENODATA. On x86_64, that is mapped to the value 61. Back on the 
sparc side, 61 is mapped to ECONNREFUSED, and that gives odd errors 
when ls tries to query xattrs:

18:20 sun:../ccgfs/src # ls -dl /home/profile
ls: /home/profile: Connection refused
drwx------ 13 cf users 4096 Aug 24 16:05 /home/profile

Just a grep away, this came up:

18:16 ichi:../linux-2.6.23/include > grep -r ENODATA .
./asm-alpha/errno.h:#define     ENODATA         86      /* No data available */
./asm-generic/errno.h:#define   ENODATA         61      /* No data available */
./asm-mips/errno.h:#define      ENODATA         61      /* No data available */
./asm-parisc/errno.h:#define    ENODATA         51      /* No data available */
./asm-sparc/errno.h:#define     ENODATA         111     /* No data available */
./asm-sparc/solerrno.h:#define  SOL_ENODATA        61    /* No data avail at this time       */
./asm-sparc64/errno.h:#define   ENODATA         111     /* No data available */
./asm-sparc64/solerrno.h:#define        SOL_ENODATA        61    /* No data avail at this time       */

Why do these architectures deviate from asm-generic? In fact,

./asm-alpha/errno.h:#define     ECONNREFUSED    61      /* Connection refused */
./asm-generic/errno.h:#define   ECONNREFUSED    111     /* Connection refused */
./asm-sparc/errno.h:#define     ECONNREFUSED    61      /* Connection refused */
./asm-sparc64/errno.h:#define   ECONNREFUSED    61      /* Connection refused */

the values are exactly swapped (mips is another oddball not portrayed 
here). Since these header files propagate into /usr/include, this 
affects userspace programs too.

So I'm just asking: can I rely on the same errno across Linuxes?
And should the errno values be fixed up?



	Jan
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Re: errno codes intertwined

[Josef Sipek]

On Fri, Aug 24, 2007 at 06:24:48PM +0200, Jan Engelhardt wrote:
...
> If a file does not have the requested attribute, the syscall will 
> produce ENODATA. On x86_64, that is mapped to the value 61. Back on the 
> sparc side, 61 is mapped to ECONNREFUSED, and that gives odd errors 
> when ls tries to query xattrs:
 
I'd think that passing the raw error code is a bad idea, and that you
probably want to have your own set of codes that you use in the trasport and
map value to/from the host's errno values.

> the values are exactly swapped (mips is another oddball not portrayed 
> here). Since these header files propagate into /usr/include, this 
> affects userspace programs too.

Yep, and it kind of sucks.

> So I'm just asking: can I rely on the same errno across Linuxes?

I wouldn't - Linux on different different architectures seems to have
different errno codes.

> And should the errno values be fixed up?

It would break userspace :-/

Josef 'Jeff' Sipek.

-- 
*NOTE: This message is ROT-13 encrypted twice for extra protection*

Re: errno codes intertwined

[Andi Kleen]

Jan Engelhardt <jengelh@computergmbh.de> writes:
> 
> So I'm just asking: can I rely on the same errno across Linuxes?

No. The errnos were originally designed to be compatible
with the "native" Unix on that platform to make running
their binaries easier. On Sparc that would
be SunOS/Solaris.

-Andi

Re: errno codes intertwined

[David Miller]

From: Jan Engelhardt <jengelh@computergmbh.de>
Date: Fri, 24 Aug 2007 18:24:48 +0200 (CEST)

> So I'm just asking: can I rely on the same errno across Linuxes?
> And should the errno values be fixed up?

You cannot rely on error numbers being the same, every
architecture has something to a few to many differences
in this area.

Re: [parisc-linux] errno codes intertwined

[Mike Frysinger]

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On Friday 24 August 2007, Jan Engelhardt wrote:
> So I'm just asking: can I rely on the same errno across Linuxes?

nope

> And should the errno values be fixed up?

i guess that depends on whether you think it's even broken :)

no spec requires any errno symbol have an exact numeric value ... i'm guessing 
your FUSE is only cross-Linux and you're not planning on dipping into any 
other OS ?
-mike

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Re: [parisc-linux] errno codes intertwined

[Jan Engelhardt]

On Aug 26 2007 13:45, Mike Frysinger wrote:
>> can I rely on the same errno across Linuxes?
>
>nope
>
>> And should the errno values be fixed up?
>
>i guess that depends on whether you think it's even broken :)
>
>no spec requires any errno symbol have an exact numeric value ... i'm guessing 
>your FUSE is only cross-Linux and you're not planning on dipping into any 
>other OS ?

If the errnos are not the same in the Linux world, it's not even
cross-Linux ;-) - but it's always translated to fixed numbers now anyway.

I have not really thought about putting it in use on other systems yet. I
don't have macosx to test, and Windows generally lacks some fuses. :^)
You are free to spin it if you like, http://freshmeat.net/p/ccgfs/


	Jan
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