1 files changed, 101 insertions, 0 deletions

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a10c8c9b6b78..de3083b0a4f5 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -74,6 +74,7 @@
 #include <linux/highmem.h>
 #include <linux/kthread.h>
 #include <linux/splice.h>
+#include <linux/sysfs.h>
 
 #include <asm/uaccess.h>
 
@@ -738,6 +739,103 @@ static inline int is_loop_device(struct file *file)
         return i && S_ISBLK(i->i_mode) && MAJOR(i->i_rdev) == LOOP_MAJOR;
 }
 
+/* loop sysfs attributes */
+
+static ssize_t loop_attr_show(struct device *dev, char *page,
+                              ssize_t (*callback)(struct loop_device *, char *))
+{
+        struct loop_device *l, *lo = NULL;
+
+        mutex_lock(&loop_devices_mutex);
+        list_for_each_entry(l, &loop_devices, lo_list)
+                if (disk_to_dev(l->lo_disk) == dev) {
+                        lo = l;
+                        break;
+                }
+        mutex_unlock(&loop_devices_mutex);
+
+        return lo ? callback(lo, page) : -EIO;
+}
+
+#define LOOP_ATTR_RO(_name)                                             \
+static ssize_t loop_attr_##_name##_show(struct loop_device *, char *);  \
+static ssize_t loop_attr_do_show_##_name(struct device *d,              \
+                                struct device_attribute *attr, char *b) \
+{                                                                       \
+        return loop_attr_show(d, b, loop_attr_##_name##_show);          \
+}                                                                       \
+static struct device_attribute loop_attr_##_name =                      \
+        __ATTR(_name, S_IRUGO, loop_attr_do_show_##_name, NULL);
+
+static ssize_t loop_attr_backing_file_show(struct loop_device *lo, char *buf)
+{
+        ssize_t ret;
+        char *p = NULL;
+
+        mutex_lock(&lo->lo_ctl_mutex);
+        if (lo->lo_backing_file)
+                p = d_path(&lo->lo_backing_file->f_path, buf, PAGE_SIZE - 1);
+        mutex_unlock(&lo->lo_ctl_mutex);
+
+        if (IS_ERR_OR_NULL(p))
+                ret = PTR_ERR(p);
+        else {
+                ret = strlen(p);
+                memmove(buf, p, ret);
+                buf[ret++] = '\n';
+                buf[ret] = 0;
+        }
+
+        return ret;
+}
+
+static ssize_t loop_attr_offset_show(struct loop_device *lo, char *buf)
+{
+        return sprintf(buf, "%llu\n", (unsigned long long)lo->lo_offset);
+}
+
+static ssize_t loop_attr_sizelimit_show(struct loop_device *lo, char *buf)
+{
+        return sprintf(buf, "%llu\n", (unsigned long long)lo->lo_sizelimit);
+}
+
+static ssize_t loop_attr_autoclear_show(struct loop_device *lo, char *buf)
+{
+        int autoclear = (lo->lo_flags & LO_FLAGS_AUTOCLEAR);
+
+        return sprintf(buf, "%s\n", autoclear ? "1" : "0");
+}
+
+LOOP_ATTR_RO(backing_file);
+LOOP_ATTR_RO(offset);
+LOOP_ATTR_RO(sizelimit);
+LOOP_ATTR_RO(autoclear);
+
+static struct attribute *loop_attrs[] = {
+        &loop_attr_backing_file.attr,
+        &loop_attr_offset.attr,
+        &loop_attr_sizelimit.attr,
+        &loop_attr_autoclear.attr,
+        NULL,
+};
+
+static struct attribute_group loop_attribute_group = {
+        .name = "loop",
+        .attrs= loop_attrs,
+};
+
+static int loop_sysfs_init(struct loop_device *lo)
+{
+        return sysfs_create_group(&disk_to_dev(lo->lo_disk)->kobj,
+                                  &loop_attribute_group);
+}
+
+static void loop_sysfs_exit(struct loop_device *lo)
+{
+        sysfs_remove_group(&disk_to_dev(lo->lo_disk)->kobj,
+                           &loop_attribute_group);
+}
+
 static int loop_set_fd(struct loop_device *lo, fmode_t mode,
                        struct block_device *bdev, unsigned int arg)
 {
@@ -837,6 +935,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 
         set_capacity(lo->lo_disk, size);
         bd_set_size(bdev, size << 9);
+        loop_sysfs_init(lo);
         /* let user-space know about the new size */
         kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
 
@@ -855,6 +954,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
         return 0;
 
 out_clr:
+        loop_sysfs_exit(lo);
         lo->lo_thread = NULL;
         lo->lo_device = NULL;
         lo->lo_backing_file = NULL;
@@ -951,6 +1051,7 @@ static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev)
         set_capacity(lo->lo_disk, 0);
         if (bdev) {
                 bd_set_size(bdev, 0);
+                loop_sysfs_exit(lo);
                 /* let user-space know about this change */
                 kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
         }