net/tap: avoid using SIGIO

SIGIO maybe used by application, instead choose another rt-signal.
Linux allows any signal to be used for signal based IO.
Search for an unused signal in the available rt-signal range.

Add more error checking for fcntl and signal handling.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>

diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
index 339f24b..b19e26b 100644 (file)
--- a/drivers/net/tap/rte_eth_tap.c
+++ b/drivers/net/tap/rte_eth_tap.c
@@ -134,7 +134,7 @@ tun_alloc(struct pmd_internals *pmd, int is_keepalive)
 #ifdef IFF_MULTI_QUEUE
        unsigned int features;
 #endif
-       int fd;
+       int fd, signo, flags;
 
        memset(&ifr, 0, sizeof(struct ifreq));
 
@@ -199,52 +199,87 @@ tun_alloc(struct pmd_internals *pmd, int is_keepalive)
                }
        }
 
+       flags = fcntl(fd, F_GETFL);
+       if (flags == -1) {
+               TAP_LOG(WARNING,
+                       "Unable to get %s current flags\n",
+                       ifr.ifr_name);
+               goto error;
+       }
+
        /* Always set the file descriptor to non-blocking */
-       if (fcntl(fd, F_SETFL, O_NONBLOCK) < 0) {
+       flags |= O_NONBLOCK;
+       if (fcntl(fd, F_SETFL, flags) < 0) {
                TAP_LOG(WARNING,
                        "Unable to set %s to nonblocking: %s",
                        ifr.ifr_name, strerror(errno));
                goto error;
        }
 
-       /* Set up trigger to optimize empty Rx bursts */
-       errno = 0;
-       do {
+       /* Find a free realtime signal */
+       for (signo = SIGRTMIN + 1; signo < SIGRTMAX; signo++) {
                struct sigaction sa;
-               int flags = fcntl(fd, F_GETFL);
 
-               if (flags == -1 || sigaction(SIGIO, NULL, &sa) == -1)
+               if (sigaction(signo, NULL, &sa) == -1) {
+                       TAP_LOG(WARNING,
+                               "Unable to get current rt-signal %d handler",
+                               signo);
+                       goto error;
+               }
+
+               /* Already have the handler we want on this signal  */
+               if (sa.sa_handler == tap_trigger_cb)
                        break;
-               if (sa.sa_handler != tap_trigger_cb) {
-                       /*
-                        * Make sure SIGIO is not already taken. This is done
-                        * as late as possible to leave the application a
-                        * chance to set up its own signal handler first.
-                        */
-                       if (sa.sa_handler != SIG_IGN &&
-                           sa.sa_handler != SIG_DFL) {
-                               errno = EBUSY;
-                               break;
-                       }
-                       sa = (struct sigaction){
-                               .sa_flags = SA_RESTART,
-                               .sa_handler = tap_trigger_cb,
-                       };
-                       if (sigaction(SIGIO, &sa, NULL) == -1)
-                               break;
+
+               /* Is handler in use by application */
+               if (sa.sa_handler != SIG_DFL) {
+                       TAP_LOG(DEBUG,
+                               "Skipping used rt-signal %d", signo);
+                       continue;
                }
-               /* Enable SIGIO on file descriptor */
-               fcntl(fd, F_SETFL, flags | O_ASYNC);
-               fcntl(fd, F_SETOWN, getpid());
-       } while (0);
 
-       if (errno) {
+               sa = (struct sigaction) {
+                       .sa_flags = SA_RESTART,
+                       .sa_handler = tap_trigger_cb,
+               };
+
+               if (sigaction(signo, &sa, NULL) == -1) {
+                       TAP_LOG(WARNING,
+                               "Unable to set rt-signal %d handler\n", signo);
+                       goto error;
+               }
+
+               /* Found a good signal to use */
+               TAP_LOG(DEBUG,
+                       "Using rt-signal %d", signo);
+               break;
+       }
+
+       if (signo == SIGRTMAX) {
+               TAP_LOG(WARNING, "All rt-signals are in use\n");
+
                /* Disable trigger globally in case of error */
                tap_trigger = 0;
-               TAP_LOG(WARNING, "Rx trigger disabled: %s",
-                       strerror(errno));
-       }
+               TAP_LOG(NOTICE, "No Rx trigger signal available\n");
+       } else {
+               /* Enable signal on file descriptor */
+               if (fcntl(fd, F_SETSIG, signo) < 0) {
+                       TAP_LOG(WARNING, "Unable to set signo %d for fd %d: %s",
+                               signo, fd, strerror(errno));
+                       goto error;
+               }
+               if (fcntl(fd, F_SETFL, flags | O_ASYNC) < 0) {
+                       TAP_LOG(WARNING, "Unable to set fcntl flags: %s",
+                               strerror(errno));
+                       goto error;
+               }
 
+               if (fcntl(fd, F_SETOWN, getpid()) < 0) {
+                       TAP_LOG(WARNING, "Unable to set fcntl owner: %s",
+                               strerror(errno));
+                       goto error;
+               }
+       }
        return fd;
 
 error: