fapolicyd: Make write() nonblocking

- switch to read only and non blocking mode for pipe
- add 1 minute loop to wait for pipe to reappear

Sometimes during the system update/upgrade fapolicyd
get restarted e.g. when systemd gets updated.
That can lead to the situation where fapolicyd pipe
has been removed and created again.
In such cases rpm-plugin-fapolicyd gets stuck on
write() to the pipe which does not exist anymore.
After switching to non blocking file descriptor
we can try to reopen the pipe if there is an error
from write(). Assuming that a new pipe should appear
when fapolicyd daemon starts again.
If not then after 1 minute of waiting we expect
fapolicyd daemon to be not active and we let the
transaction continue.

Signed-off-by: Radovan Sroka <rsroka@redhat.com>

plugins/fapolicyd.c

@@ -27,7 +27,7 @@ static rpmRC open_fifo(struct fapolicyd_data* state)
     int fd = -1;
     struct stat s;
 
-    fd = open(state->fifo_path, O_RDWR);
+    fd = open(state->fifo_path, O_WRONLY|O_NONBLOCK);
     if (fd == -1) {
         rpmlog(RPMLOG_DEBUG, "Open: %s -> %s\n", state->fifo_path, strerror(errno));
         goto bad;
@@ -55,15 +55,26 @@ static rpmRC open_fifo(struct fapolicyd_data* state)
     }
 
     state->fd = fd;
+
     /* considering success */
     return RPMRC_OK;
 
  bad:
     if (fd >= 0)
         close(fd);
+
+    state->fd = -1;
     return RPMRC_FAIL;
 }
 
+static void close_fifo(struct fapolicyd_data* state)
+{
+    if (state->fd > 0)
+        (void) close(state->fd);
+
+    state->fd = -1;
+}
+
 static rpmRC write_fifo(struct fapolicyd_data* state, const char * str)
 {
     ssize_t len = strlen(str);
@@ -86,6 +97,54 @@ static rpmRC write_fifo(struct fapolicyd_data* state, const char * str)
     return RPMRC_FAIL;
 }
 
+static void try_to_write_to_fifo(struct fapolicyd_data* state, const char * str)
+{
+    int reload = 0;
+    int printed = 0;
+
+    /* 1min/60s */
+    const int timeout = 60;
+
+    /* wait up to X seconds */
+    for (int i = 0; i < timeout; i++) {
+
+        if (reload) {
+            if (!printed) {
+                rpmlog(RPMLOG_WARNING, "rpm-plugin-fapolicyd: waiting for the service connection to resume, it can take up to %d seconds\n", timeout);
+                printed = 1;
+            }
+
+            (void) close_fifo(state);
+            (void) open_fifo(state);
+        }
+
+        if (state->fd >= 0) {
+            if (write_fifo(state, str) == RPMRC_OK) {
+
+                /* write was successful after few reopens */
+                if (reload)
+                    rpmlog(RPMLOG_WARNING, "rpm-plugin-fapolicyd: the service connection has resumed\n");
+
+                break;
+            }
+        }
+
+        /* failed write or reopen */
+        reload = 1;
+        sleep(1);
+
+        /* the last iteration */
+        /* consider failure */
+        if (i == timeout-1) {
+            rpmlog(RPMLOG_WARNING, "rpm-plugin-fapolicyd: the service connection has not resumed\n");
+            rpmlog(RPMLOG_WARNING, "rpm-plugin-fapolicyd: continuing without the service\n");
+        }
+
+    }
+
+}
+
+
 static rpmRC fapolicyd_init(rpmPlugin plugin, rpmts ts)
 {
     if (rpmtsFlags(ts) & (RPMTRANS_FLAG_TEST|RPMTRANS_FLAG_BUILD_PROBS))
@@ -102,10 +161,7 @@ static rpmRC fapolicyd_init(rpmPlugin plugin, rpmts ts)
 
 static void fapolicyd_cleanup(rpmPlugin plugin)
 {
-    if (fapolicyd_state.fd > 0)
-        (void) close(fapolicyd_state.fd);
-
-    fapolicyd_state.fd = -1;
+    (void) close_fifo(&fapolicyd_state);
 }
 
 static rpmRC fapolicyd_tsm_post(rpmPlugin plugin, rpmts ts, int res)
@@ -116,9 +172,9 @@ static rpmRC fapolicyd_tsm_post(rpmPlugin plugin, rpmts ts, int res)
     /* we are ready */
     if (fapolicyd_state.fd > 0) {
         /* send a signal that transaction is over */
-        (void) write_fifo(&fapolicyd_state, "1\n");
+        (void) try_to_write_to_fifo(&fapolicyd_state, "1\n");
         /* flush cache */
-        (void) write_fifo(&fapolicyd_state, "2\n");
+        (void) try_to_write_to_fifo(&fapolicyd_state, "2\n");
     }
 
  end:
@@ -133,7 +189,7 @@ static rpmRC fapolicyd_scriptlet_pre(rpmPlugin plugin, const char *s_name,
 
     if (fapolicyd_state.changed_files > 0) {
         /* send signal to flush cache */
-        (void) write_fifo(&fapolicyd_state, "2\n");
+        (void) try_to_write_to_fifo(&fapolicyd_state, "2\n");
 
         /* optimize flushing */
         /* flush only when there was an actual change */
@@ -176,7 +232,7 @@ static rpmRC fapolicyd_fsm_file_prepare(rpmPlugin plugin, rpmfi fi,
     char * sha = rpmfiFDigestHex(fi, NULL);
 
     snprintf(buffer, 4096, "%s %lu %64s\n", dest, size, sha);
-    (void) write_fifo(&fapolicyd_state, buffer);
+    (void) try_to_write_to_fifo(&fapolicyd_state, buffer);
 
     free(sha);