Re: EINTR vs ERESTARTSYS, ERESTARTSYS not defined

[Andreas Schwab <schwab@suse.de>]

Phil Howard <phil-linux-kernel@ipal.net> writes:

|> The accept() call does indeed return errno==ERESTARTSYS to user space
|> when coming back from signal handling, even though other things like
|> poll() return errno==EINTR.  This would not really be a problem except
|> for this in include/linux/errno.h starting at line 6:
|> 
|> +=============================================================================
|> | #ifdef __KERNEL__
|> | 
|> | /* Should never be seen by user programs */
|> | #define ERESTARTSYS     512
|> | #define ERESTARTNOINTR  513
|> | #define ERESTARTNOHAND  514     /* restart if no handler.. */
|> | #define ENOIOCTLCMD     515     /* No ioctl command */
|> +=============================================================================
|> 
|> So which way is it _supposed_ to be (so someone can patch things up
|> to make it consistent):
|> 
|> 1.  User space should never see ERESTARTSYS from any system call

Yes.  The kernel either transforms it to EINTR, or restarts the syscall
when the signal handler returns.

|> 2.  ERESTARTSYS can be seen from system call and is defined somewhere
|> 
|> In user space I have to define __KERNEL__ to get programs to compile
|> when coded to know about all possible (valid?) values of errno from
|> system calls.  As seen from strace:

strace is special here, because it gets more information than the traced
program would get.

|> +=============================================================================
|> | [pid  6453] accept(5, 0xbffff908, [16]) = ? ERESTARTSYS (To be restarted)

At this point the accept syscall hasn't actually finished yet, but rather
suspended to let the program execute the signal handler.  As soon as the
signal handler returns the syscall will be restarted.

Andreas.

-- 
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