[stgt] [PATCH v2] redirect: protect again tgtd process hang as of cluster software hang

[Or Gerlitz]

commit fb0bd886021239aac72bb34a497af0cca946f1e7
Author: Or Gerlitz <ogerlitz at mellanox.com>
Date:   Thu Mar 17 15:22:30 2011 +0200

    redirect: protect again tgtd process hang as of cluster software hang

    If the child process spawned to run the redirect callback script hangs, e.g
    as of load/bug in the application which this script is dealing with, tgt
    can hang forever. Protect against that by selecting the fd from which tgt
    is expected to read, for up to 100ms, if the timeout expires, tgt terminates
    the child process and fail the initiator login attempt. While not being the
    ultimate solution, of using tgt_event_add et al. and making the redirect
    code fully asynchronous, this patch adds protection and makes things much
    better in that respect.

    Signed-off-by: Alexander Nezhinsky <alexandern at mellanox.com>
    Signed-off-by: Or Gerlitz <ogerlitz at mellanox.com>
-----

added a comment and few formatting changes

diff --git a/usr/tgtd.c b/usr/tgtd.c
index 946cd3e..4f71e1e 100644
--- a/usr/tgtd.c
+++ b/usr/tgtd.c
@@ -319,7 +319,24 @@ int call_program(const char *cmd, void (*callback)(void *data, int result),
 		eprintf("execv failed for: %s, %m\n", cmd);
 		exit(-1);
 	} else {
+		struct timeval tv;
+		fd_set rfds;
+		int ret_sel;
+
 		close(fds[1]);
+		/* 0.1 second is okay, as the initiator will retry anyway */
+		do {
+			FD_ZERO(&rfds);
+			FD_SET(fds[0],&rfds);
+			tv.tv_sec = 0;
+			tv.tv_usec = 100000;
+			ret_sel = select(fds[0]+1, &rfds, NULL, NULL, &tv);
+		} while (ret_sel < 0 && errno == EINTR);
+		if (ret_sel <= 0) { /* error or timeout */
+			eprintf("timeout on redirect callback, \
+					terminating child pid %d\n", pid);
+			kill(pid, SIGTERM);
+		}
 		do {
 			ret = waitpid(pid, &i, 0);
 		} while (ret < 0 && errno == EINTR);
@@ -328,11 +345,13 @@ int call_program(const char *cmd, void (*callback)(void *data, int result),
 			close(fds[0]);
 			return ret;
 		}
-		ret = read(fds[0], output, op_len);
-		if (ret < 0) {
-			eprintf("failed to get the output from: %s\n", cmd);
-			close(fds[0]);
-			return ret;
+		if (ret_sel > 0) {
+			ret = read(fds[0], output, op_len);
+			if (ret < 0) {
+				eprintf("failed to get the output from: %s\n", cmd);
+				close(fds[0]);
+				return ret;
+			}
 		}

 		if (callback)

--
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