[CRIU] [PATCH] fdstore: Print detailed error when queue is exhausted

[Cyrill Gorcunov]

We use fdstore intensively for example when handling
bindmounted sockets and ghost dgram sockets. The system
limit for per-socket queue may not be enough if someone
generate lots of ghost sockets (150 and more as been
detected on default fedora 27).

We can't just increase system limits since thery are
global but instead lets print an error with list
of parameters to adjust. This will give a node
admin a way to process restore.

Signed-off-by: Cyrill Gorcunov <gorcunov at gmail.com>
---
 criu/fdstore.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/criu/fdstore.c b/criu/fdstore.c
index 8d3a6c89b1dc..2748c6743fa7 100644
--- a/criu/fdstore.c
+++ b/criu/fdstore.c
@@ -79,11 +79,25 @@ int fdstore_init(void)
 int fdstore_add(int fd)
 {
 	int sk = get_service_fd(FDSTORE_SK_OFF);
-	int id;
+	int id, ret, i;
 
 	mutex_lock(&desc->lock);
 
-	if (send_fd(sk, NULL, 0, fd)) {
+	ret = send_fd(sk, NULL, 0, fd);
+	if (ret) {
+		int err_cpy = errno;
+		pr_perror("Can't send fd %d into store\n", fd);
+		if (err_cpy == EAGAIN) {
+			static const char * const sysctl_params[] = {
+				"net.core.rmem_default",
+				"net.core.rmem_max",
+				"net.core.wmem_default",
+				"net.core.wmem_max",
+			};
+			pr_err("Too many fdstore entries are used. Increase sysctl:\n");
+			for (i = 0; i < ARRAY_SIZE(sysctl_params); i++)
+				pr_err("  %s\n", sysctl_params[i]);
+		}
 		mutex_unlock(&desc->lock);
 		return -1;
 	}
-- 
2.14.4