1 files changed, 120 insertions, 0 deletions
diff --git a/src/lock.c b/src/lock.c
new file mode 100644
index 0000000..48c409f
--- /dev/null
+++ b/src/lock.c
@@ -0,0 +1,120 @@
+#include <unistd.h>
+#include <sys/stat.h>
+#include <stdio.h>
+#include <limits.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <libdaemon/dlog.h>
+
+#include "lock.h"
+
+/* Where do lockfiles reside? */
+#define LOCK_PATH "/var/lock"
+
+static const char *lockfile(const char *dev) {
+    static char lockfile[PATH_MAX];
+    snprintf(lockfile, sizeof(lockfile), "%s/LCK..%s", LOCK_PATH, basename(dev));
+    return lockfile;
+}
+
+static const char *tempfile(const char *path) {
+    static char t[PATH_MAX];
+    snprintf(t, sizeof(t), "%s.tmp.%lu", path, (unsigned long) getpid());
+    return t;
+}
+
+int device_lock(const char *dev) {
+    struct stat st;
+    int fd;
+    char *path, *temp;
+    char buf[100];
+
+    if (stat(LOCK_PATH, &st) != 0 || !S_ISDIR(st.st_mode)) {
+        daemon_log(LOG_ERR, "Failed to lock device, directory "LOCK_PATH" not existent.");
+        return -1;
+    }
+
+    path = lockfile(dev);
+    temp = tempfile(path);
+
+    for (;;) {
+        
+        if ((fd = open(path, O_RDONLY)) < 0) {
+            if (errno != ENOENT) {
+                daemon_log(LOG_ERR, "Failed to open lock file: %s", strerror(errno));
+                return -1;
+            }
+        }
+        
+        if (fd >= 0) {
+            ssize_t n;
+
+            n = loop_read(fd, buf, sizeof(buf) - 1);
+            close(fd);
+
+            if (n < 0) {
+                close(fd)
+                daemon_log(LOG_ERR, "Failed to read from lock file: %s", strerror(errno));
+                return -1;
+            }
+            
+            if (n > 0) {
+                pid_t pid;
+                
+                if (n == 4)
+                    pid = (pid_t) *((uint32_t*) buf);
+                else {
+                    buf[n] = 0;
+                    sscanf(buf, "%lu", &pid);
+                }
+                
+                if (pid > 0) {
+                    if (kill(pid, 0) < 0 && errno == ESRCH) {
+                        daemon_log(LOG_WARN, "Lockfile is stale. Overriding it.");
+                        /* Yes, here is a race condition */
+                        unlink(path);
+                    } else
+                        return 1;
+                }
+            }
+        }
+        
+        if ((fd = open(temp, O_WRONLY | O_CREAT | O_EXCL, 0666)) < 0) {
+            daemon_log(LOG_ERR, "Failed to create temporary lock file: %s", strerror(errno));
+            return -1;
+        }
+
+        snprintf(buf, sizeof(buf), "%10lu %s %.20s\n", (unsigned long) getpid(), appname, username);
+        if (loop_write(fd, buf, strlen(buf)) < 0) {
+            daemon_log(LOG_ERR, "Failed to write to temporary lock file: %s", sterror(errno));
+            close(fd);
+            return -1;
+        }
+    
+        close(fd);
+
+        if (link(temp, path) < 0) {
+            if (errno == EEXIST)
+                continue;
+
+            daemon_log(LOG_ERR, "Failed to link temporary lock file: %s", strerror(errno));
+        }
+
+
+        return 0;
+    }
+}
+
+int device_unlock(const char *dev) {
+
+    if (unlink(lockfile(dev)) < 0) {
+        daemon_log(LOG_ERR, "Failed to remove lock file: %s", strerror(errno));
+        return -1;
+    }
+
+    return 0;
+}