Marin D wrote:
> Could someone give me some light on the SA_RESTART flag used by
> sigaction() as the man page and the *info file contain contrary
> information
>
> [snip from the man page]
>
> SA_RESTART
> The opposite to SA_ONESHOT, do not restore
> the signal action. This provides behavior
> compatible with BSD signal semantics.
This is wrong. To get the opposite behaviour to SA_ONESHOT (i.e. BSD
semantics), simply don't specify SA_ONESHOT.
It's not what my sigaction(2) manpage says, either:
SA_RESTART
Provide behaviour compatible with BSD signal
semantics by making certain system calls
restartable across signals.
> This seems to be right. I tested it. The SA_RESTART makes the signal
> action not be changed with the default action once raised.
No, it's the lack of SA_ONESHOT that causes the signal disposition not
to be reset to its default.
> [snip from the libc info file]
>
> - Macro: int SA_RESTART
> This flag controls what happens when a signal is delivered during
> certain primitives (such as `open', `read' or `write'), and the
> signal handler returns normally. There are two alternatives: the
> library function can resume, or it can return failure with error
> code `EINTR'.
>
> The choice is controlled by the `SA_RESTART' flag for the
> particular kind of signal that was delivered. If the flag is set,
> returning from a handler resumes the library function. If the
> flag is clear, returning from a handler makes the function fail.
This is correct. SA_RESTART => BSD semantics, no SA_RESTART => SysV
semantics.
> Well.. I have no idea how to raise signal during open() and to test
> this...
Install a handler for SIGALRM, use alarm() to cause a SIGALRM to be
generated after a given delay, and then perform an open() on a tty
device or FIFO.
> So , why is the info contrary and is the man page correct as I think?
No, the man page is wrong.
> And how to acquire behaviour as explained by the *info file i.e. to make
> i/o functions "atomic" in the way of resuming operation and not returning
> EINTR?
Specify SA_RESTART.
Basically to get the behaviour of BSD's signal() function, you set the
`sa_flags' field to SA_RESTART, whereas to get the behaviour of the
SysV signal() function, you would set it to (SA_ONESHOT | SA_NODEFER).
--
Glynn Clements <[EMAIL PROTECTED]>
