[systemd-devel] [PATCH] vconsole-setup.c: prevent EIO failure

[harald at redhat.com]

From: Harald Hoyer <harald at redhat.com>

There might be a race condition that happens if you try to open
/dev/tty0 while the current TTY is currently being closed.
This would yield an -EIO error.
---
 src/vconsole-setup.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/src/vconsole-setup.c b/src/vconsole-setup.c
index 1be260b..60a5f14 100644
--- a/src/vconsole-setup.c
+++ b/src/vconsole-setup.c
@@ -176,7 +176,21 @@ int main(int argc, char **argv) {
         else
                 vc = "/dev/tty0";
 
+again:
         if ((fd = open(vc, O_RDWR|O_CLOEXEC)) < 0) {
+                if (errno == EIO) {
+                        /* Linux can return EIO if the tty is currently closing,
+                         * which can happen if multiple processes are opening and
+                         * closing the console in parallel. Unfortunately it can
+                         * also return EIO in more serious situations too (see
+                         * https://bugs.launchpad.net/bugs/554172), but there isn't
+                         * much we can do about that since we really need a console
+                         * fd.
+                         */
+                        struct timespec ts = { 0, 100000000 }; /* 0.1 seconds */
+                        nanosleep (&ts, NULL);
+                        goto again;
+                }
                 log_error("Failed to open %s: %m", vc);
                 goto finish;
         }
-- 
1.7.3.4