[Xen-devel] [PATCH V2] xenconsole: add file lock to xenconsole

[Yufang Zhang <yufang521247@xxxxxxxxx>]

From: Yufang Zhang <yuzhang@xxxxxxxxxx>

This patch add a file lock to xenconsole for each console id, so
that only one console could be attached to a guest at a time.
Otherwise, consoles would get stuck and print strange outputs.

The version2 patch fix bellow problems:
1) fix for indent level and coding style as the surrounding code
2) put the lock files in /var/run/
3) use snprintf instead of sprintf

Considering the lock files are just blank files and they can be
reused, leaving them behind when xenconsole crashes(or killed by
kill -9) is not so bad.

Signed-off-by: Yufang Zhang <yufang521247@xxxxxxxxx>
---
 tools/console/client/main.c |   31 +++++++++++++++++++++++++++++++
 1 files changed, 31 insertions(+), 0 deletions(-)

diff --git a/tools/console/client/main.c b/tools/console/client/main.c
index df3636f..ff1c64e 100644
--- a/tools/console/client/main.c
+++ b/tools/console/client/main.c
@@ -46,6 +46,28 @@
 
 static volatile sig_atomic_t received_signal = 0;
 
+static int console_locked(const char *file)
+{
+       int fd;
+
+       fd = open(file, O_RDWR | O_CREAT, S_IRUSR|S_IWUSR);
+       if (fd == -1) {
+               fprintf(stderr,"can't open lock file: %s\n", file);
+               exit(1);
+       }
+
+       if (lockf(fd, F_TLOCK, 0) == -1) {
+               if ( errno == EACCES || errno == EAGAIN ) {
+                       close(fd);
+                       return (1);
+               }
+               fprintf(stderr,"can't lock file: %s\n", file);
+               exit(1);
+       }
+
+       return (0);
+}
+
 static void sighandler(int signum)
 {
        received_signal = 1;
@@ -280,6 +302,7 @@ int main(int argc, char **argv)
        int spty, xsfd;
        struct xs_handle *xs;
        char *end;
+       char buf[100];
        console_type type = CONSOLE_INVAL;
 
        while((ch = getopt_long(argc, argv, sopt, lopt, &opt_ind)) != -1) {
@@ -368,6 +391,13 @@ int main(int argc, char **argv)
                exit(EINVAL);
        }
 
+       /* Make sure only one console is attached to guest */
+       snprintf(buf, strlen("/var/run/xenconsole-%d-%d") + 1, 
"/var/run/xenconsole-%d-%d", domid, num);
+       if (console_locked(buf) == 1) {
+               fprintf(stderr, "Another console has already been attached to 
guest\n");
+               exit(EINVAL);
+       }
+
        /* Set a watch on this domain's console pty */
        if (!xs_watch(xs, path, ""))
                err(errno, "Can't set watch for console pty");
@@ -387,6 +417,7 @@ int main(int argc, char **argv)
        console_loop(spty, xs, path);
        restore_term(STDIN_FILENO, &attr);
 
+       unlink(buf);
        free(path);
        free(dom_path);
        return 0;
-- 
1.7.4.4


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel