Hi Rajat,
On Tue, Jan 11, 2011 at 9:26 PM, Rajat Sharma <fs.rajat@xxxxxxxxx> wrote:
> Hi Dave,
>
> My understanding was based out of linux/errno.h. Maybe the below
> comment is in context of glibc abstracting out ERESTART* error codes.
>
> #ifdef __KERNEL__
>
> /*
> * These should never be seen by user programs. To return one of ERESTART*
> * codes, signal_pending() MUST be set. Note that ptrace can observe these
> * at syscall exit tracing, but they will never be left for the debugged user
> * process to see.
> */
> #define ERESTARTSYS 512
> #define ERESTARTNOINTR 513
> #define ERESTARTNOHAND 514 /* restart if no handler.. */
> #define ENOIOCTLCMD 515 /* No ioctl command */
> #define ERESTART_RESTARTBLOCK 516 /* restart by calling sys_restart_syscall */
Yeah - that's consistent with my understanding. The code flow would be
something like this
user-mode program calls ioctl
ioctl does some stuff
signal happens
ioctl detects signal (typically by a call returning -EINTR) and
decides to return -ERESTARTSYS
sys handler detects pending signal
user-mode signal handler is called
sys handler re-issues ioctl
ioctl does some stuff
ioctl returns normally
user mode program sees normal reutrn code
So ioctl returns -ERESTARTSYS, but the user mode program is completely
oblivious to the fact that this happened.
glibc doesn't even get to know that the -ERESTARTSYS code was returned
by ioctl. It gets intercepted and processed by the kernel.
Dave Hylands
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