[Xen-devel] [PATCH v2] libvchan: tidy up usages of fcntl in select-type sample application

[Matthew Daley <mattjd@xxxxxxxxx>]

Namely, don't overwrite all the other flags when twiddling O_NONBLOCK,
and add basic error handling.

Coverity-ID: 1055041
Signed-off-by: Matthew Daley <mattjd@xxxxxxxxx>
---
v2: Adjust other fcntl usage further down as well. Use F_GETFL to modify
only the O_NONBLOCK flag. Both suggested by Daniel De Graaf.
Improve commit message.

 tools/libvchan/node-select.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/tools/libvchan/node-select.c b/tools/libvchan/node-select.c
index 6c6c19e..acd9bae 100644
--- a/tools/libvchan/node-select.c
+++ b/tools/libvchan/node-select.c
@@ -90,6 +90,7 @@ int main(int argc, char **argv)
 {
        int ret;
        int libxenvchan_fd;
+       int flags;
        if (argc < 4 || argv[3][0] != '/')
                usage(argv);
        if (!strcmp(argv[1], "server")) {
@@ -105,8 +106,13 @@ int main(int argc, char **argv)
                exit(1);
        }
 
-       fcntl(0, F_SETFL, O_NONBLOCK);
-       fcntl(1, F_SETFL, O_NONBLOCK);
+       if ((flags = fcntl(0, F_GETFL)) == -1 ||
+               fcntl(0, F_SETFL, flags | O_NONBLOCK) == -1 ||
+               (flags = fcntl(1, F_GETFL)) == -1 ||
+               fcntl(1, F_SETFL, flags | O_NONBLOCK) == -1) {
+               perror("fcntl");
+               exit(1);
+       }
 
        libxenvchan_fd = libxenvchan_fd_for_select(ctrl);
        for (;;) {
@@ -153,7 +159,11 @@ int main(int argc, char **argv)
                        stdout_wr();
                }
                if (!libxenvchan_is_open(ctrl)) {
-                       fcntl(1, F_SETFL, 0);
+                       if ((flags = fcntl(1, F_GETFL)) == -1 ||
+                               fcntl(1, F_SETFL, flags & ~O_NONBLOCK) == -1) {
+                               perror("fcntl");
+                               exit(1);
+                       }
                        while (outsiz)
                                stdout_wr();
                        return 0;
-- 
1.7.10.4


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