Re: Use enum to declare errno values

From: linux-os (Dick Johnson)
Date: Wed Nov 23 2005 - 09:19:39 EST

On Wed, 23 Nov 2005, moreau francis wrote:

> Hi,
> I'm just wondering why not declaring errno values using enumaration ?
> It is just more convenient when debuging the kernel.
> Thanks

There is an attempt to keep kernel errno values similar to
user-mode errno values. This simplifies the user-kernel
interface where the kernel will return -ERRNO and the user-mode
code negates it and puts it into the user errno then sets the
return value to -1 (a Unix convention).

The user-mode errno's therefore must correspond. You can't
expect the 'C' runtime libraries to be rebuilt and/or all the
programs recompiled just because the kernel got changed so
the errno's are hard-coded. 0 will always mean "no error" and
1 will always be EPERM, etc. There are error-codes that are
the same number also, EWOULDBLOCK and EAGAIN are examples.

So, you can't just auto-enumerate. If auto-enumeration isn't
possible, then you might just as well use #define, which is
what is done.

Dick Johnson
Penguin : Linux version on an i686 machine (5589.55 BogoMips).
Warning : 98.36% of all statistics are fiction.

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