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authorNicolas S. Dade <nic.dade@gmail.com>2015-12-19 03:39:19 (GMT)
committerWaldemar Brodkorb <wbx@uclibc-ng.org>2015-12-22 13:32:50 (GMT)
commite3c3bf2b5801d0cc544e732fcee1ba51121051b3 (patch)
treeba569e54011048dc82264ffa1953a6293c90bd9d
parentf5bdd8ff82607e55a1c511e13e37a984408c8094 (diff)
pselect: Use linux pselect syscall when available
Linux has a pselect syscall since 2.6.something. Using it rather than emulating it with sigprocmask+select+sigprocmask is smaller code, and works properly. (The emulation has race conditions when unblocked signals arrive before or after the select) The tv.nsec >= 1E9 handling comes from uclibc's linux select() implementation, which itself uses pselect() internally if the pselect syscall exists. I though it would be good to do the same here. Note that although the libc pselect() API has 6 arguments, the linux kernel syscall as 7 arguments. There is an extra, somewhat vestigial, sizeof the signal mask argument. Signed-off-by: Nicolas S. Dade <nic.dade@gmail.com>
-rw-r--r--libc/sysdeps/linux/common/pselect.c52
1 files changed, 52 insertions, 0 deletions
diff --git a/libc/sysdeps/linux/common/pselect.c b/libc/sysdeps/linux/common/pselect.c
index bf19ce3..3f1dd28 100644
--- a/libc/sysdeps/linux/common/pselect.c
+++ b/libc/sysdeps/linux/common/pselect.c
@@ -30,6 +30,57 @@ static int __NC(pselect)(int nfds, fd_set *readfds, fd_set *writefds,
fd_set *exceptfds, const struct timespec *timeout,
const sigset_t *sigmask)
{
+#ifdef __NR_pselect6
+#define NSEC_PER_SEC 1000000000L
+ struct timespec _ts, *ts = 0;
+ if (timeout) {
+ /* The Linux kernel can in some situations update the timeout value.
+ * We do not want that so use a local variable.
+ */
+ _ts = *timeout;
+
+ /* GNU extension: allow for timespec values where the sub-sec
+ * field is equal to or more than 1 second. The kernel will
+ * reject this on us, so take care of the time shift ourself.
+ * Some applications (like readline and linphone) do this.
+ * See 'clarification on select() type calls and invalid timeouts'
+ * on the POSIX general list for more information.
+ */
+ if (_ts.tv_nsec >= NSEC_PER_SEC) {
+ _ts.tv_sec += _ts.tv_nsec / NSEC_PER_SEC;
+ _ts.tv_nsec %= NSEC_PER_SEC;
+ }
+
+ ts = &_ts;
+ }
+
+ /* The pselect6 syscall API is strange. It wants a 7th arg to be
+ * the sizeof(*sigmask). However syscalls with > 6 arguments aren't
+ * supported on linux. So arguments 6 and 7 are stuffed in a struct
+ * and a pointer to that struct is passed as the 6th argument to
+ * the syscall.
+ * Glibc stuffs arguments 6 and 7 in a ulong[2]. Linux reads
+ * them as if there were a struct { sigset_t*; size_t } in
+ * userspace. There woudl be trouble if userspace and the kernel are
+ * compiled differently enough that size_t isn't the same as ulong,
+ * but not enough to trigger the compat layer in linux. I can't
+ * think of such a case, so I'm using linux's struct.
+ * Furthermore Glibc sets the sigsetsize to _NSIG/8. However linux
+ * checks for sizeof(sigset_t), which internally is a ulong array.
+ * This means that if _NSIG isn't a multiple of BITS_PER_LONG then
+ * linux will refuse glibc's value. So I prefer sizeof(sigset_t) for
+ * the value of sigsetsize.
+ */
+ struct {
+ const sigset_t *sigmask;
+ size_t sigsetsize;
+ } args67 = {
+ sigmask,
+ sizeof(sigset_t),
+ };
+
+ return INLINE_SYSCALL(pselect6, 6, nfds, readfds, writefds, exceptfds, ts, &args67);
+#else
struct timeval tval;
int retval;
sigset_t savemask;
@@ -57,6 +108,7 @@ static int __NC(pselect)(int nfds, fd_set *readfds, fd_set *writefds,
sigprocmask (SIG_SETMASK, &savemask, NULL);
return retval;
+#endif
}
CANCELLABLE_SYSCALL(int, pselect, (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
const struct timespec *timeout, const sigset_t *sigmask),