errno

errno

[Albert Cahalan]

Linus Torvalds writes:

> No, there's something wrong. Nobody should use a global
> "errno" variable, and we should fix the real bug (it's
> probably some buggy system call "interface" function
> that is being used).

According to lib/errno.c it's your fault. (SCO code?)

The obvious fix would be to stuff errno into the
task_struct, hmmm? Then just add this:

#define errno (current->kernel_errno)

Otherwise:

#define errno   Do not use this.

Re: errno

[Linus Torvalds]

On Mon, 3 May 2004, Albert Cahalan wrote:
> 
> The obvious fix would be to stuff errno into the
> task_struct, hmmm?

No. "errno" is one of those fundamentally broken things that should not 
exist. It was wrogn in original UNIX, it's wrong now.

The kernel usage comes not from the kernel wanting to use it per se (the 
kernel has always used the "negative error" approach), but from some 
misguided kernel modules using the user-space interfaces.

The Linux way of returning negative error numbers is much nicer. It's
inherently thread-safe, and it has no performance downsides. Of course, it
does depend on having enough of a result domain that you can always
separate error returns from good returns, but that's true in practice for
all system calls.

Too bad we can't fix broken calling conventions.

		Linus

Re: errno

[Philippe Troin]

Linus Torvalds <torvalds@osdl.org> writes:

> On Mon, 3 May 2004, Albert Cahalan wrote:
> > 
> > The obvious fix would be to stuff errno into the
> > task_struct, hmmm?
> 
> No. "errno" is one of those fundamentally broken things that should not 
> exist. It was wrogn in original UNIX, it's wrong now.
> 
> The kernel usage comes not from the kernel wanting to use it per se (the 
> kernel has always used the "negative error" approach), but from some 
> misguided kernel modules using the user-space interfaces.
> 
> The Linux way of returning negative error numbers is much nicer. It's
> inherently thread-safe, and it has no performance downsides. Of course, it
> does depend on having enough of a result domain that you can always
> separate error returns from good returns, but that's true in practice for
> all system calls.

Except of course for fcntl(fd, F_GETOWN) where the owner is a
(negative) process group... If the owning process group has a "low
enough" PGID, it collides with errors and glibc reports an error and
sets errno to -PGID. One might argue that in this instance, that the
BSD's overloading of the pid field with pgids is at fault, but the bug
still remains :-)

Phil.

Re: errno

[Philippe Troin]

Philippe Troin <phil@fifi.org> writes:

> Linus Torvalds <torvalds@osdl.org> writes:
> 
> > On Mon, 3 May 2004, Albert Cahalan wrote:
> > > 
> > > The obvious fix would be to stuff errno into the
> > > task_struct, hmmm?
> > 
> > No. "errno" is one of those fundamentally broken things that should not 
> > exist. It was wrogn in original UNIX, it's wrong now.
> > 
> > The kernel usage comes not from the kernel wanting to use it per se (the 
> > kernel has always used the "negative error" approach), but from some 
> > misguided kernel modules using the user-space interfaces.
> > 
> > The Linux way of returning negative error numbers is much nicer. It's
> > inherently thread-safe, and it has no performance downsides. Of course, it
> > does depend on having enough of a result domain that you can always
> > separate error returns from good returns, but that's true in practice for
> > all system calls.
> 
> Except of course for fcntl(fd, F_GETOWN) where the owner is a
> (negative) process group... If the owning process group has a "low
> enough" PGID, it collides with errors and glibc reports an error and
> sets errno to -PGID. One might argue that in this instance, that the
> BSD's overloading of the pid field with pgids is at fault, but the bug
> still remains :-)

This is a patch against 2.6.5 for what I am talking about. Of course,
glibc needs to be patched as well to transparently issue a
F_GETOWN_ARG when the user requests F_GETOWN...

Phil.

diff -rcN linux-2.6.5.orig/fs/fcntl.c linux-2.6.5/fs/fcntl.c
*** linux-2.6.5.orig/fs/fcntl.c	Sat Apr  3 19:37:36 2004
--- linux-2.6.5/fs/fcntl.c	Wed May  5 18:06:02 2004
***************
*** 323,328 ****
--- 323,339 ----
  			err = filp->f_owner.pid;
  			force_successful_syscall_return();
  			break;
+ 		case F_GETOWN_ARG:
+ 			/*
+ 			 * Works around F_GETOWN's return limitations.
+ 			 * Libc will transparently convert F_GETOWN to 
+ 			 * F_GETOWN_ARG.
+ 			 */
+ 			err = 0;
+ 			if (copy_to_user(&filp->f_owner.pid, (void*)arg, 
+ 					 sizeof(filp->f_owner.pid)))
+ 				err = -EFAULT;
+ 			break;
  		case F_SETOWN:
  			err = f_setown(filp, arg, 1);
  			break;
diff -rcN linux-2.6.5.orig/include/asm-alpha/fcntl.h linux-2.6.5/include/asm-alpha/fcntl.h
*** linux-2.6.5.orig/include/asm-alpha/fcntl.h	Sat Apr  3 19:37:24 2004
--- linux-2.6.5/include/asm-alpha/fcntl.h	Wed May  5 17:57:03 2004
***************
*** 36,41 ****
--- 36,43 ----
  #define F_SETSIG	10	/*  for sockets. */
  #define F_GETSIG	11	/*  for sockets. */
  
+ #define F_GETOWN_ARG	12	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-arm/fcntl.h linux-2.6.5/include/asm-arm/fcntl.h
*** linux-2.6.5.orig/include/asm-arm/fcntl.h	Sat Apr  3 19:36:27 2004
--- linux-2.6.5/include/asm-arm/fcntl.h	Wed May  5 17:56:51 2004
***************
*** 39,44 ****
--- 39,46 ----
  #define F_SETLK64	13
  #define F_SETLKW64	14
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-arm26/fcntl.h linux-2.6.5/include/asm-arm26/fcntl.h
*** linux-2.6.5.orig/include/asm-arm26/fcntl.h	Sat Apr  3 19:37:40 2004
--- linux-2.6.5/include/asm-arm26/fcntl.h	Wed May  5 17:56:47 2004
***************
*** 39,44 ****
--- 39,46 ----
  #define F_SETLK64	13
  #define F_SETLKW64	14
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-cris/fcntl.h linux-2.6.5/include/asm-cris/fcntl.h
*** linux-2.6.5.orig/include/asm-cris/fcntl.h	Sat Apr  3 19:36:25 2004
--- linux-2.6.5/include/asm-cris/fcntl.h	Wed May  5 17:56:41 2004
***************
*** 41,46 ****
--- 41,48 ----
  #define F_SETLK64      13
  #define F_SETLKW64     14
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-h8300/fcntl.h linux-2.6.5/include/asm-h8300/fcntl.h
*** linux-2.6.5.orig/include/asm-h8300/fcntl.h	Sat Apr  3 19:37:43 2004
--- linux-2.6.5/include/asm-h8300/fcntl.h	Wed May  5 17:56:37 2004
***************
*** 39,44 ****
--- 39,46 ----
  #define F_SETLK64	13
  #define F_SETLKW64	14
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-i386/fcntl.h linux-2.6.5/include/asm-i386/fcntl.h
*** linux-2.6.5.orig/include/asm-i386/fcntl.h	Sat Apr  3 19:37:23 2004
--- linux-2.6.5/include/asm-i386/fcntl.h	Wed May  5 17:56:21 2004
***************
*** 39,44 ****
--- 39,46 ----
  #define F_SETLK64	13
  #define F_SETLKW64	14
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-ia64/fcntl.h linux-2.6.5/include/asm-ia64/fcntl.h
*** linux-2.6.5.orig/include/asm-ia64/fcntl.h	Sat Apr  3 19:37:23 2004
--- linux-2.6.5/include/asm-ia64/fcntl.h	Wed May  5 17:56:11 2004
***************
*** 43,48 ****
--- 43,50 ----
  #define F_SETSIG	10	/*  for sockets. */
  #define F_GETSIG	11	/*  for sockets. */
  
+ #define F_GETOWN_ARG	12	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-m68k/fcntl.h linux-2.6.5/include/asm-m68k/fcntl.h
*** linux-2.6.5.orig/include/asm-m68k/fcntl.h	Sat Apr  3 19:36:53 2004
--- linux-2.6.5/include/asm-m68k/fcntl.h	Wed May  5 17:55:57 2004
***************
*** 39,44 ****
--- 39,46 ----
  #define F_SETLK64	13
  #define F_SETLKW64	14
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-mips/fcntl.h linux-2.6.5/include/asm-mips/fcntl.h
*** linux-2.6.5.orig/include/asm-mips/fcntl.h	Sat Apr  3 19:37:43 2004
--- linux-2.6.5/include/asm-mips/fcntl.h	Wed May  5 17:55:36 2004
***************
*** 42,47 ****
--- 42,48 ----
  #define F_GETOWN	23	/*  for sockets. */
  #define F_SETSIG	10	/*  for sockets. */
  #define F_GETSIG	11	/*  for sockets. */
+ #define F_GETOWN_ARG	25	/*  same as F_GETOWN, but uses arg */
  
  #ifndef __mips64
  #define F_GETLK64	33	/*  using 'struct flock64' */
diff -rcN linux-2.6.5.orig/include/asm-parisc/fcntl.h linux-2.6.5/include/asm-parisc/fcntl.h
*** linux-2.6.5.orig/include/asm-parisc/fcntl.h	Sat Apr  3 19:37:07 2004
--- linux-2.6.5/include/asm-parisc/fcntl.h	Wed May  5 17:55:10 2004
***************
*** 42,47 ****
--- 42,48 ----
  #define F_SETOWN	12	/*  for sockets. */
  #define F_SETSIG	13	/*  for sockets. */
  #define F_GETSIG	14	/*  for sockets. */
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
  
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
diff -rcN linux-2.6.5.orig/include/asm-ppc/fcntl.h linux-2.6.5/include/asm-ppc/fcntl.h
*** linux-2.6.5.orig/include/asm-ppc/fcntl.h	Sat Apr  3 19:37:07 2004
--- linux-2.6.5/include/asm-ppc/fcntl.h	Wed May  5 17:54:59 2004
***************
*** 39,44 ****
--- 39,46 ----
  #define F_SETLK64	13
  #define F_SETLKW64	14
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-ppc64/fcntl.h linux-2.6.5/include/asm-ppc64/fcntl.h
*** linux-2.6.5.orig/include/asm-ppc64/fcntl.h	Sat Apr  3 19:36:15 2004
--- linux-2.6.5/include/asm-ppc64/fcntl.h	Wed May  5 17:54:51 2004
***************
*** 42,47 ****
--- 42,49 ----
  #define F_SETSIG	10	/*  for sockets. */
  #define F_GETSIG	11	/*  for sockets. */
  
+ #define F_GETOWN_ARG	12	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-s390/fcntl.h linux-2.6.5/include/asm-s390/fcntl.h
*** linux-2.6.5.orig/include/asm-s390/fcntl.h	Sat Apr  3 19:36:12 2004
--- linux-2.6.5/include/asm-s390/fcntl.h	Wed May  5 17:54:43 2004
***************
*** 48,53 ****
--- 48,55 ----
  #define F_SETLKW64	14
  #endif /* ! __s390x__ */
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-sh/fcntl.h linux-2.6.5/include/asm-sh/fcntl.h
*** linux-2.6.5.orig/include/asm-sh/fcntl.h	Sat Apr  3 19:37:42 2004
--- linux-2.6.5/include/asm-sh/fcntl.h	Wed May  5 17:54:29 2004
***************
*** 39,44 ****
--- 39,46 ----
  #define F_SETLK64	13
  #define F_SETLKW64	14
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-sparc/fcntl.h linux-2.6.5/include/asm-sparc/fcntl.h
*** linux-2.6.5.orig/include/asm-sparc/fcntl.h	Sat Apr  3 19:38:20 2004
--- linux-2.6.5/include/asm-sparc/fcntl.h	Wed May  5 17:54:23 2004
***************
*** 39,44 ****
--- 39,46 ----
  #define F_SETLK64	13
  #define F_SETLKW64	14
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-sparc64/fcntl.h linux-2.6.5/include/asm-sparc64/fcntl.h
*** linux-2.6.5.orig/include/asm-sparc64/fcntl.h	Sat Apr  3 19:38:20 2004
--- linux-2.6.5/include/asm-sparc64/fcntl.h	Wed May  5 17:54:18 2004
***************
*** 35,40 ****
--- 35,41 ----
  #define F_SETLKW	9
  #define F_SETSIG	10	/*  for sockets. */
  #define F_GETSIG	11	/*  for sockets. */
+ #define F_GETOWN_ARG	12	/*  same as F_GETOWN, but uses arg */
  
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
diff -rcN linux-2.6.5.orig/include/asm-v850/fcntl.h linux-2.6.5/include/asm-v850/fcntl.h
*** linux-2.6.5.orig/include/asm-v850/fcntl.h	Sat Apr  3 19:36:53 2004
--- linux-2.6.5/include/asm-v850/fcntl.h	Wed May  5 17:53:58 2004
***************
*** 39,44 ****
--- 39,46 ----
  #define F_SETLK64	13
  #define F_SETLKW64	14
  
+ #define F_GETOWN_ARG	15	/*  same as F_GETOWN, but uses arg */
+ 
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
  
diff -rcN linux-2.6.5.orig/include/asm-x86_64/fcntl.h linux-2.6.5/include/asm-x86_64/fcntl.h
*** linux-2.6.5.orig/include/asm-x86_64/fcntl.h	Sat Apr  3 19:36:26 2004
--- linux-2.6.5/include/asm-x86_64/fcntl.h	Wed May  5 17:53:48 2004
***************
*** 34,39 ****
--- 34,40 ----
  #define F_GETOWN	9	/*  for sockets. */
  #define F_SETSIG	10	/*  for sockets. */
  #define F_GETSIG	11	/*  for sockets. */
+ #define F_GETOWN_ARG	12	/*  same as F_GETOWN, but uses arg */
  
  /* for F_[GET|SET]FL */
  #define FD_CLOEXEC	1	/* actually anything with low bit set goes */