libudev: implement udev_device_set_attribute_value()

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>

1 files changed, 102 insertions, 0 deletions

diff --git a/src/libudev/libudev-device.c b/src/libudev/libudev-device.c
index 3c9783ffd8..fd3e694ef6 100644
--- a/src/libudev/libudev-device.c
+++ b/src/libudev/libudev-device.c
@@ -1535,6 +1535,108 @@ out:
         return ret;
 }
 
+/**
+ * udev_device_set_sysattr_value:
+ * @udev_device: udev device
+ * @sysattr: attribute name
+ * @value: new value to be set
+ *
+ * Update the contents of the sys attribute and the cached value of the device.
+ *
+ * Returns: Negative error code on failure or 0 on success.
+ **/
+_public_ int udev_device_set_sysattr_value(struct udev_device *udev_device, const char *sysattr, char *value)
+{
+        struct udev_device *dev;
+        char path[UTIL_PATH_SIZE];
+        struct stat statbuf;
+        int fd;
+        ssize_t size, value_len;
+        int ret = 0;
+
+        if (udev_device == NULL)
+                return -EINVAL;
+        dev = udev_device;
+        if (sysattr == NULL)
+                return -EINVAL;
+        if (value == NULL)
+                value_len = 0;
+        else
+                value_len = strlen(value);
+restart:
+        strscpyl(path, sizeof(path), udev_device_get_syspath(dev), "/", sysattr, NULL);
+        if (lstat(path, &statbuf) != 0) {
+                udev_list_entry_add(&dev->sysattr_value_list, sysattr, NULL);
+                ret = -ENXIO;
+                goto out;
+        }
+
+        if (S_ISLNK(statbuf.st_mode)) {
+                /*
+                 * Cannot modify core link values
+                 */
+                if (streq(sysattr, "driver") ||
+                    streq(sysattr, "subsystem") ||
+                    streq(sysattr, "module")) {
+                        ret = -EPERM;
+                } else if (!streq(sysattr, "device")) {
+                        /* resolve custom link to a device */
+                        strscpyl(path, sizeof(path), udev_device->syspath, "/", sysattr, NULL);
+                        dev = udev_device_new_from_syspath(udev_device->udev, path);
+                        if (dev != NULL)
+                                goto restart;
+                        ret = -ENXIO;
+                } else {
+                        /* Unhandled, to not try to modify anything */
+                        ret = -EINVAL;
+                }
+                goto out;
+        }
+
+        /* skip directories */
+        if (S_ISDIR(statbuf.st_mode)) {
+                ret = -EISDIR;
+                goto out;
+        }
+
+        /* skip non-readable files */
+        if ((statbuf.st_mode & S_IRUSR) == 0) {
+                ret = -EACCES;
+                goto out;
+        }
+
+        /* Value is limited to 4k */
+        if (value_len > 4096) {
+                ret = -EINVAL;
+                goto out;
+        }
+        util_remove_trailing_chars(value, '\n');
+
+        /* write attribute value */
+        fd = open(path, O_WRONLY|O_CLOEXEC);
+        if (fd < 0) {
+                ret = -errno;
+                goto out;
+        }
+        size = write(fd, value, value_len);
+        close(fd);
+        if (size < 0) {
+                ret = -errno;
+                goto out;
+        }
+        if (size < value_len) {
+                ret = -EIO;
+                goto out;
+        }
+
+        /* wrote a valid value, store it in cache and return it */
+        udev_list_entry_add(&dev->sysattr_value_list, sysattr, value);
+out:
+        if (dev != udev_device)
+                udev_device_unref(dev);
+        return ret;
+}
+
 static int udev_device_sysattr_list_read(struct udev_device *udev_device)
 {
         struct dirent *dent;