Hi folks
I've been playing with yet unseen prd block device, and hit an issue with
partitioning
but since prd.c is a copy/paste of brd.c the same exact issue exists with brd.
It does not support partitions!
An attempt to fdisk say a couple of partitions, then mkfs && mount an individual
partition will result in the primary device being accessed and a corrupted disk
data.
If I enable max_part(=2) properly on modprobe, then fdisk a couple of
partitions all
goes well
But then if I pass the device to Kernel (Say via mount), after a call to
bdev = blkdev_get_by_path(dev_name, mode, fs_type);
I get the following results:
(size is extracted using: i_size_read(bdev->bd_inode);
part_size is extracted using: bdev->bd_part->nr_sects << 9;
)
dev_name == /dev/ram0
[Jul29 17:40] foo: [foo_mount:880] size=0x40000000 bdev=ffff88003dc24340
bd_inode=ffff88003dc24430 bd_part=ffff88003ca22848 part_size=0x40000000
dev_name == /dev/ram0p1
[ +16.816065] foo: [foo_mount:880] size=0x40000000 bdev=ffff88003d2f6d80
bd_inode=ffff88003d2f6e70 bd_part=ffff88003ca22848 part_size=0x40000000
dev_name == /dev/ram0p2
[Jul29 17:41] foo: [foo_mount:880] size=0x40000000 bdev=ffff88003dc24680
bd_inode=ffff88003dc24770 bd_part=ffff88003ca22848 part_size=0x40000000
We can see that all 3 different bdev's point to the same bd_part, which is the
BUG. Funny is that bd_inode is different but contains
same wrong size, for exactly the same reason.
The fix for this is easy:
----
diff --git drivers/block/brd.c drivers/block/brd.c
index c7d138e..0d982d7 100644
--- drivers/block/brd.c
+++ drivers/block/brd.c
@@ -378,10 +378,12 @@ static int brd_direct_access(struct block_device *bdev,
sector_t sector,
if (!brd)
return -ENODEV;
+ sector += get_start_sect(bdev);
if (sector & (PAGE_SECTORS-1))
return -EINVAL;
+/* Check is wrong here we need to check against bdev->bd_part->nr_sects */
if (sector + PAGE_SECTORS > get_capacity(bdev->bd_disk))
return -ERANGE;
page = brd_insert_page(brd, sector);
if (!page)
return -ENOSPC;
@@ -532,11 +532,17 @@ static struct brd_device *brd_init_one(int i)
goto out;
}
+/* In the structure of this driver this will never happen and is wrong
+ * to do. We should just return NULL if not found.
+ * This is not the bug it is just DEAD CODE
+ *
brd = brd_alloc(i);
if (brd) {
add_disk(brd->brd_disk);
list_add_tail(&brd->brd_list, &brd_devices);
}
+*/
+ prd = NULL;
out:
return brd;
}
@@ -558,7 +564,8 @@ static struct kobject *brd_probe(dev_t dev, int *part, void
*data)
kobj = brd ? get_disk(brd->brd_disk) : NULL;
mutex_unlock(&brd_devices_mutex);
- *part = 0;
+// Fix the partition BUG *part comes in correctly must not need to touch it
+// *part = 0;
return kobj;
}
---
After this simple fix of commenting out *part = 0, running again I get
dev_name == /dev/ram0
[ +0.000004] foo: [foo_mount:880] size=0x40000000 bdev=ffff88003d2f7740
inode=ffff88003d2f7830 part=ffff88001da8c048 part_size=0x40000000
dev_name == /dev/ram0p1
[ +0.000002] foo: [foo_mount:880] size=0x1e748200 bdev=ffff88003dc25040
inode=ffff88003dc25130 part=ffff880036f6a000 part_size=0x1e748200
dev_name == /dev/ram0p2
[ +0.000002] foo: [foo_mount:880] size=0x217b7e00 bdev=ffff88003d2f7a80
inode=ffff88003d2f7b70 part=ffff880036f69000 part_size=0x217b7e00
But before we are running to fix this bug. Could we please do better and just
remove the support for partitions
all together.
Since it *never* worked anyway, so probably no one needs it! Surly no
one used it
Thanks
Boaz
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