[PATCH] xfree86: Use SA_SIGINFO if available for SIGIO handlers

[Adam Jackson]

This one's slightly subtle, the fcntl(F_SETSIG) is required for ->si_fd
to actually be filled in correctly, at least on Linux.  I know this area
has been sensitive to platform variation in the past, so I'd appreciate
a second look from Solaris / BSD / Hurd people.

---

siginfo_t gives us the file descriptor that raised the signal directly,
so we don't need to select() for it.  This gets evdev event processing
down to exactly one syscall in the common case.

Signed-off-by: Adam Jackson <ajax at redhat.com>
---
 hw/xfree86/os-support/shared/sigio.c |   40 ++++++++++++++++++++++++++++-----
 1 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/hw/xfree86/os-support/shared/sigio.c b/hw/xfree86/os-support/shared/sigio.c
index aed5654..4f1ec55 100644
--- a/hw/xfree86/os-support/shared/sigio.c
+++ b/hw/xfree86/os-support/shared/sigio.c
@@ -95,12 +95,11 @@ static int		xf86SigIOMax;
 static int		xf86SigIOMaxFd;
 static fd_set		xf86SigIOMask;
 
-/*
- * SIGIO gives no way of discovering which fd signalled, select
- * to discover
- */
+#ifndef SA_SIGINFO
+
+/* plain signals have no way of discovering which fd signalled. */
 static void
-xf86SIGIO (int sig)
+sigio_handler (int sig)
 {
     int	    i;
     fd_set  ready;
@@ -126,6 +125,27 @@ xf86SIGIO (int sig)
     errno = save_errno;
 }
 
+#else /* have SA_SIGINFO */
+
+/* siginfo passes the triggering fd in, no need to select() */
+static void
+sigio_sigaction(int sig, siginfo_t *si, void *ctx)
+{
+    int i;
+    int save_errno = errno;
+
+    for (i = 0; i < MAX_FUNCS; i++) {
+        if (xf86SigIOFuncs[i].f && xf86SigIOFuncs[i].fd == si->si_fd) {
+            (*xf86SigIOFuncs[i].f)(si->si_fd, xf86SigIOFuncs[i].closure);
+            break;
+        }
+    }
+
+    errno = save_errno;
+}
+
+#endif
+
 static int
 xf86IsPipe (int fd)
 {
@@ -164,6 +184,9 @@ xf86InstallSIGIOHandler(int fd, void (*f)(int, void *), void *closure)
 		    xf86Msg(X_WARNING, "fcntl(%d, F_SETOWN): %s\n",
 			    fd, strerror(errno));
 		} else {
+#ifdef SA_SIGINFO
+                    fcntl(fd, F_SETSIG, SIGIO);
+#endif
 		    installed = TRUE;
 		}
 	    }
@@ -184,8 +207,13 @@ xf86InstallSIGIOHandler(int fd, void (*f)(int, void *), void *closure)
 	    }
 	    sigemptyset(&sa.sa_mask);
 	    sigaddset(&sa.sa_mask, SIGIO);
+#ifndef SA_SIGINFO
 	    sa.sa_flags   = 0;
-	    sa.sa_handler = xf86SIGIO;
+	    sa.sa_handler = sigio_handler;
+#else
+            sa.sa_flags     = SA_SIGINFO;
+            sa.sa_sigaction = sigio_sigaction;
+#endif
 	    sigaction(SIGIO, &sa, &osa);
 	    xf86SigIOFuncs[i].fd = fd;
 	    xf86SigIOFuncs[i].closure = closure;
-- 
1.6.5.2