[PATCH] mdadm:reminded external bitmap only supports ext[2-4] filesystem

mdadm: ensure that the external bitmap_file is
stored by ext[2-4] file system, because bmap()
of linux/driver/md/bitmap.c only implements in
inode.c of ext[2-4]. it's better to make users
aware of this scenario and give a prompt.

steps:
zlliu:/home/liu/git-tree/mdadm # df -T /mnt/2
Filesystem     Type  1K-blocks     Used Available Use% Mounted on
/dev/sda5      btrfs 103078176 11110620  90902628  11% /

./mdadm -CR /dev/md0 -l1 -b /mnt/2 -n2 /dev/loop[0-1]

Signed-off-by: Zhilong Liu <redacted>
---
 Create.c |  5 -----
 mdadm.c  | 15 +++++++++++++++
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/Create.c b/Create.c
index 50ec85e..beec29f 100644
--- a/Create.c
+++ b/Create.c

@@ -827,11 +827,6 @@ int Create(struct supertype *st, char *mddev,
 			goto abort_locked;
 		}
 		bitmap_fd = open(s->bitmap_file, O_RDWR);
-		if (bitmap_fd < 0) {
-			pr_err("weird: %s cannot be openned\n",
-				s->bitmap_file);
-			goto abort_locked;
-		}
 		if (ioctl(mdfd, SET_BITMAP_FILE, bitmap_fd) < 0) {
 			pr_err("Cannot set bitmap file for %s: %s\n",
 				mddev, strerror(errno));

diff --git a/mdadm.c b/mdadm.c
index fcb33d1..566051f 100644
--- a/mdadm.c
+++ b/mdadm.c

@@ -1149,6 +1149,21 @@ int main(int argc, char *argv[])
 			    strcmp(optarg, "none") == 0 ||
 			    strchr(optarg, '/') != NULL) {
 				s.bitmap_file = optarg;
+				if (strchr(s.bitmap_file, '/') != NULL) {
+					bitmap_fd = open(s.bitmap_file, O_RDWR);
+					if (bitmap_fd < 0) {
+						pr_err("weird: %s cannot be openned\n", s.bitmap_file);
+						exit(2);
+					}
+					close(bitmap_fd);
+					struct statfs ext_bitmap;
+					statfs(s.bitmap_file, &ext_bitmap);
+					if (ext_bitmap.f_type != 0xEF53){
+						pr_err("external bitmap only supports ext[2-4] filesystem, %s.\n",
+							s.bitmap_file);
+						exit(2);
+					}
+				}
 				continue;
 			}
 			if (strcmp(optarg, "clustered") == 0) {

-- 
2.6.6

On 03/20/2017 01:20 PM, Zhilong Liu wrote:

mdadm: ensure that the external bitmap_file is
stored by ext[2-4] file system, because bmap()
of linux/driver/md/bitmap.c only implements in
inode.c of ext[2-4]. it's better to make users
aware of this scenario and give a prompt.

steps:
zlliu:/home/liu/git-tree/mdadm # df -T /mnt/2
Filesystem     Type  1K-blocks     Used Available Use% Mounted on
/dev/sda5      btrfs 103078176 11110620  90902628  11% /

./mdadm -CR /dev/md0 -l1 -b /mnt/2 -n2 /dev/loop[0-1]

   as the purpose to improve the prompt when using external bitmap
mode, actually I disagree this patch for mdadm, it doesn't need to do
this action in userland.
   For errno rule, bmap() returned EINVAL indeed, but finally mdadm
received the EINVAL by RUN_ARRAY.
   I think it would be more user-friendly if prints one prompt and returned
EINVAL at the same time when the bmap() got failure, so that user can
be easy to know where the EINVAL comes.
Such as:

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 9fb2cca..0bff96b 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c

@@ -381,6 +381,7 @@ static int read_page(struct file *file, unsigned 

long index,
                         bh->b_blocknr = bmap(inode, block);
                         if (bh->b_blocknr == 0) {
                                 /* Cannot use this file! */
+                               pr_err("external bitmap only supports to 
write into a ext[2-4] file.\n");
                                 ret = -EINVAL;
                                 goto out;
                         }

    keep waiting for your comments for this scenario.

Thanks,
-Zhilong