2 files changed, 46 insertions, 4 deletions

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 936cac3c3126..b336433f8157 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -724,7 +724,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
                 goto out_putf;
 
         fput(old_file);
-        if (max_part > 0)
+        if (lo->lo_flags & LO_FLAGS_PARTSCAN)
                 ioctl_by_bdev(bdev, BLKRRPART, 0);
         return 0;
 
@@ -808,16 +808,25 @@ static ssize_t loop_attr_autoclear_show(struct loop_device *lo, char *buf)
         return sprintf(buf, "%s\n", autoclear ? "1" : "0");
 }
 
+static ssize_t loop_attr_partscan_show(struct loop_device *lo, char *buf)
+{
+        int partscan = (lo->lo_flags & LO_FLAGS_PARTSCAN);
+
+        return sprintf(buf, "%s\n", partscan ? "1" : "0");
+}
+
 LOOP_ATTR_RO(backing_file);
 LOOP_ATTR_RO(offset);
 LOOP_ATTR_RO(sizelimit);
 LOOP_ATTR_RO(autoclear);
+LOOP_ATTR_RO(partscan);
 
 static struct attribute *loop_attrs[] = {
         &loop_attr_backing_file.attr,
         &loop_attr_offset.attr,
         &loop_attr_sizelimit.attr,
         &loop_attr_autoclear.attr,
+        &loop_attr_partscan.attr,
         NULL,
 };
 
@@ -979,7 +988,9 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
         }
         lo->lo_state = Lo_bound;
         wake_up_process(lo->lo_thread);
-        if (max_part > 0)
+        if (part_shift)
+                lo->lo_flags |= LO_FLAGS_PARTSCAN;
+        if (lo->lo_flags & LO_FLAGS_PARTSCAN)
                 ioctl_by_bdev(bdev, BLKRRPART, 0);
         return 0;
 
@@ -1070,7 +1081,6 @@ static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev)
         lo->lo_offset = 0;
         lo->lo_sizelimit = 0;
         lo->lo_encrypt_key_size = 0;
-        lo->lo_flags = 0;
         lo->lo_thread = NULL;
         memset(lo->lo_encrypt_key, 0, LO_KEY_SIZE);
         memset(lo->lo_crypt_name, 0, LO_NAME_SIZE);
@@ -1088,8 +1098,11 @@ static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev)
         lo->lo_state = Lo_unbound;
         /* This is safe: open() is still holding a reference. */
         module_put(THIS_MODULE);
-        if (max_part > 0 && bdev)
+        if (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev)
                 ioctl_by_bdev(bdev, BLKRRPART, 0);
+        lo->lo_flags = 0;
+        if (!part_shift)
+                lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
         mutex_unlock(&lo->lo_ctl_mutex);
         /*
          * Need not hold lo_ctl_mutex to fput backing file.
@@ -1159,6 +1172,13 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
              (info->lo_flags & LO_FLAGS_AUTOCLEAR))
                 lo->lo_flags ^= LO_FLAGS_AUTOCLEAR;
 
+        if ((info->lo_flags & LO_FLAGS_PARTSCAN) &&
+             !(lo->lo_flags & LO_FLAGS_PARTSCAN)) {
+                lo->lo_flags |= LO_FLAGS_PARTSCAN;
+                lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
+                ioctl_by_bdev(lo->lo_device, BLKRRPART, 0);
+        }
+
         lo->lo_encrypt_key_size = info->lo_encrypt_key_size;
         lo->lo_init[0] = info->lo_init[0];
         lo->lo_init[1] = info->lo_init[1];
@@ -1654,6 +1674,27 @@ static struct loop_device *loop_alloc(int i)
         if (!disk)
                 goto out_free_queue;
 
+        /*
+         * Disable partition scanning by default. The in-kernel partition
+         * scanning can be requested individually per-device during its
+         * setup. Userspace can always add and remove partitions from all
+         * devices. The needed partition minors are allocated from the
+         * extended minor space, the main loop device numbers will continue
+         * to match the loop minors, regardless of the number of partitions
+         * used.
+         *
+         * If max_part is given, partition scanning is globally enabled for
+         * all loop devices. The minors for the main loop devices will be
+         * multiples of max_part.
+         *
+         * Note: Global-for-all-devices, set-only-at-init, read-only module
+         * parameteters like 'max_loop' and 'max_part' make things needlessly
+         * complicated, are too static, inflexible and may surprise
+         * userspace tools. Parameters like this in general should be avoided.
+         */
+        if (!part_shift)
+                disk->flags |= GENHD_FL_NO_PART_SCAN;
+        disk->flags |= GENHD_FL_EXT_DEVT;
         mutex_init(&lo->lo_ctl_mutex);
         lo->lo_number           = i;
         lo->lo_thread           = NULL;
diff --git a/include/linux/loop.h b/include/linux/loop.h
index 66c194e2d9b9..4367fc507fe9 100644
--- a/include/linux/loop.h
+++ b/include/linux/loop.h
@@ -76,6 +76,7 @@ enum {
         LO_FLAGS_READ_ONLY      = 1,
         LO_FLAGS_USE_AOPS       = 2,
         LO_FLAGS_AUTOCLEAR      = 4,
+        LO_FLAGS_PARTSCAN       = 8,
 };
 
 #include <asm/posix_types.h>    /* for __kernel_old_dev_t */