pstree: Ignore processes that disappear before reading cmdline

The worst case here is that the user has specific a PID on the
command-line, read_proc() fails to read cmdline for an irrelevant,
transient process and fails.

It is better to simply ignore processes that have disappeared.  That
way pstree can provide useful output in more cases.

An alternative is to read cmdline only for processes that the user is
interested in.  However, this probably increases the chances of an
interesting process exiting before the cmdline is read.

Signed-off-by: Martin Schwenke <martin@meltin.net>

1 files changed, 15 insertions, 5 deletions

diff --git a/src/pstree.c b/src/pstree.c
index b5b71cd..5540fe2 100644
--- a/src/pstree.c
+++ b/src/pstree.c
@@ -941,12 +941,22 @@ static void read_proc(void)
               else {
                 sprintf(path, "%s/%d/cmdline", PROC_BASE, pid);
                 if ((fd = open(path, O_RDONLY)) < 0) {
-                  perror(path);
-                  exit(1);
-                }
+		  /* If this fails then the process is gone.  If a PID
+		   * was specified on the command-line then we might
+		   * not even be interested in the current process.
+		   * There's no sensible way of dealing with this race
+		   * so we might as well behave as if the current
+		   * process did not exist.  */
+		  (void) fclose(file);
+		  free(path);
+		  continue;
+		}
                 if ((size = read(fd, buffer, buffer_size)) < 0) {
-                  perror(path);
-                  exit(1);
+			/* As above. */
+		  close(fd);
+		  (void) fclose(file);
+		  free(path);
+		  continue;
                 }
                 (void) close(fd);
                 /* If we have read the maximum screen length of args, bring it back by one to stop overflow */