Reduce timeout to zero when running inside a container

Detect container environments and set timeout to zero unless
ZFS_MODULE_TIMEOUT is already set. This avoids an unnecessary ten
second delay after running zfs/zpool commands in a container where
/dev/zfs is unavailable.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Adi Gollamudi <adigollamudi@gmail.com>
Closes #15165
Closes #17922

lib/libzfs/os/linux/libzfs_util_os.c

@@ -78,6 +78,38 @@ libzfs_error_init(int error)
 	}
 }
 
+static int
+in_container(void)
+{
+	char buffer[4096];
+	ssize_t count;
+	int fd;
+
+	if (access("/run/systemd/container", R_OK) == 0)
+		return (1);
+
+	fd = open("/proc/1/cgroup", O_RDONLY);
+	if (fd == -1)
+		return (0);
+
+	count = read(fd, buffer, sizeof (buffer) - 1);
+	close(fd);
+
+	if (count <= 0)
+		return (0);
+
+	buffer[count] = '\0';
+
+	if (strstr(buffer, "docker") ||
+	    strstr(buffer, "containerd") ||
+	    strstr(buffer, "kubepods") ||
+	    strstr(buffer, "lxc")) {
+		return (1);
+	}
+
+	return (0);
+}
+
 /*
  * zfs(4) is loaded by udev if there's a fstype=zfs device present,
  * but if there isn't, load them automatically;
@@ -104,6 +136,11 @@ libzfs_load_module(void)
 
 	const char *timeout_str = getenv("ZFS_MODULE_TIMEOUT");
 	int seconds = 10;
+
+	/* Set timeout to zero if inside of a container */
+	if (in_container())
+		seconds = 0;
+
 	if (timeout_str)
 		seconds = MIN(strtol(timeout_str, NULL, 0), 600);
 	struct itimerspec timeout = {.it_value.tv_sec = MAX(seconds, 0)};