3 files changed, 73 insertions, 2 deletions

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index c7784a985676..ac688fb54e1d 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -1934,6 +1934,44 @@ location_store(struct mddev *mddev, const char *buf, size_t len)
 static struct md_sysfs_entry bitmap_location =
 __ATTR(location, S_IRUGO|S_IWUSR, location_show, location_store);
 
+/* 'bitmap/space' is the space available at 'location' for the
+ * bitmap.  This allows the kernel to know when it is safe to
+ * resize the bitmap to match a resized array.
+ */
+static ssize_t
+space_show(struct mddev *mddev, char *page)
+{
+        return sprintf(page, "%lu\n", mddev->bitmap_info.space);
+}
+
+static ssize_t
+space_store(struct mddev *mddev, const char *buf, size_t len)
+{
+        unsigned long sectors;
+        int rv;
+
+        rv = kstrtoul(buf, 10, &sectors);
+        if (rv)
+                return rv;
+
+        if (sectors == 0)
+                return -EINVAL;
+
+        if (mddev->bitmap &&
+            sectors  < ((mddev->bitmap->file_pages - 1) * PAGE_SIZE
+                        + mddev->bitmap->last_page_size + 511) >> 9)
+                return -EFBIG; /* Bitmap is too big for this small space */
+
+        /* could make sure it isn't too big, but that isn't really
+         * needed - user-space should be careful.
+         */
+        mddev->bitmap_info.space = sectors;
+        return len;
+}
+
+static struct md_sysfs_entry bitmap_space =
+__ATTR(space, S_IRUGO|S_IWUSR, space_show, space_store);
+
 static ssize_t
 timeout_show(struct mddev *mddev, char *page)
 {
@@ -2109,6 +2147,7 @@ __ATTR(max_backlog_used, S_IRUGO | S_IWUSR,
 
 static struct attribute *md_bitmap_attrs[] = {
         &bitmap_location.attr,
+        &bitmap_space.attr,
         &bitmap_timeout.attr,
         &bitmap_backlog.attr,
         &bitmap_chunksize.attr,
diff --git a/drivers/md/md.c b/drivers/md/md.c
index ac99616f48d4..9a677f2078a7 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1197,7 +1197,10 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *rdev)
                 mddev->dev_sectors = ((sector_t)sb->size) * 2;
                 mddev->events = ev1;
                 mddev->bitmap_info.offset = 0;
+                mddev->bitmap_info.space = 0;
+                /* bitmap can use 60 K after the 4K superblocks */
                 mddev->bitmap_info.default_offset = MD_SB_BYTES >> 9;
+                mddev->bitmap_info.default_space = 64*2 - (MD_SB_BYTES >> 9);
                 mddev->reshape_backwards = 0;
 
                 if (mddev->minor_version >= 91) {
@@ -1234,9 +1237,12 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *rdev)
                 mddev->max_disks = MD_SB_DISKS;
 
                 if (sb->state & (1<<MD_SB_BITMAP_PRESENT) &&
-                    mddev->bitmap_info.file == NULL)
+                    mddev->bitmap_info.file == NULL) {
                         mddev->bitmap_info.offset =
                                 mddev->bitmap_info.default_offset;
+                        mddev->bitmap_info.space =
+                                mddev->bitmap_info.space;
+                }
 
         } else if (mddev->pers == NULL) {
                 /* Insist on good event counter while assembling, except
@@ -1677,7 +1683,12 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
                 mddev->dev_sectors = le64_to_cpu(sb->size);
                 mddev->events = ev1;
                 mddev->bitmap_info.offset = 0;
+                mddev->bitmap_info.space = 0;
+                /* Default location for bitmap is 1K after superblock
+                 * using 3K - total of 4K
+                 */
                 mddev->bitmap_info.default_offset = 1024 >> 9;
+                mddev->bitmap_info.default_space = (4096-1024) >> 9;
                 mddev->reshape_backwards = 0;
 
                 mddev->recovery_cp = le64_to_cpu(sb->resync_offset);
@@ -1686,9 +1697,23 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
                 mddev->max_disks =  (4096-256)/2;
 
                 if ((le32_to_cpu(sb->feature_map) & MD_FEATURE_BITMAP_OFFSET) &&
-                    mddev->bitmap_info.file == NULL )
+                    mddev->bitmap_info.file == NULL) {
                         mddev->bitmap_info.offset =
                                 (__s32)le32_to_cpu(sb->bitmap_offset);
+                        /* Metadata doesn't record how much space is available.
+                         * For 1.0, we assume we can use up to the superblock
+                         * if before, else to 4K beyond superblock.
+                         * For others, assume no change is possible.
+                         */
+                        if (mddev->minor_version > 0)
+                                mddev->bitmap_info.space = 0;
+                        else if (mddev->bitmap_info.offset > 0)
+                                mddev->bitmap_info.space =
+                                        8 - mddev->bitmap_info.offset;
+                        else
+                                mddev->bitmap_info.space =
+                                        -mddev->bitmap_info.offset;
+                }
 
                 if ((le32_to_cpu(sb->feature_map) & MD_FEATURE_RESHAPE_ACTIVE)) {
                         mddev->reshape_position = le64_to_cpu(sb->reshape_position);
@@ -5280,6 +5305,7 @@ static void md_clean(struct mddev *mddev)
         mddev->merge_check_needed = 0;
         mddev->bitmap_info.offset = 0;
         mddev->bitmap_info.default_offset = 0;
+        mddev->bitmap_info.default_space = 0;
         mddev->bitmap_info.chunksize = 0;
         mddev->bitmap_info.daemon_sleep = 0;
         mddev->bitmap_info.max_write_behind = 0;
@@ -6076,6 +6102,7 @@ static int set_array_info(struct mddev * mddev, mdu_array_info_t *info)
         set_bit(MD_CHANGE_DEVS, &mddev->flags);
 
         mddev->bitmap_info.default_offset = MD_SB_BYTES >> 9;
+        mddev->bitmap_info.default_space = 64*2 - (MD_SB_BYTES >> 9);
         mddev->bitmap_info.offset = 0;
 
         mddev->reshape_position = MaxSector;
@@ -6258,6 +6285,8 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
                                 return -EINVAL;
                         mddev->bitmap_info.offset =
                                 mddev->bitmap_info.default_offset;
+                        mddev->bitmap_info.space =
+                                mddev->bitmap_info.default_space;
                         mddev->pers->quiesce(mddev, 1);
                         rv = bitmap_create(mddev);
                         if (!rv)
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 360937389e64..7b4a3c318cae 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -393,10 +393,13 @@ struct mddev {
                                                  * For external metadata, offset
                                                  * from start of device. 
                                                  */
+                unsigned long           space; /* space available at this offset */
                 loff_t                  default_offset; /* this is the offset to use when
                                                          * hot-adding a bitmap.  It should
                                                          * eventually be settable by sysfs.
                                                          */
+                unsigned long           default_space; /* space available at
+                                                        * default offset */
                 struct mutex            mutex;
                 unsigned long           chunksize;
                 unsigned long           daemon_sleep; /* how many jiffies between updates? */