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block: add partition resize function to blkpg ioctl

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Add a new operation code (BLKPG_RESIZE_PARTITION) to the BLKPG ioctl that
allows altering the size of an existing partition, even if it is currently
in use.

This patch converts hd_struct->nr_sects into sequence counter because
One might extend a partition while IO is happening to it and update of
nr_sects can be non-atomic on 32bit machines with 64bit sector_t. This
can lead to issues like reading inconsistent size of a partition. Sequence
counter have been used so that readers don't have to take bdev mutex lock
as we call sector_in_part() very frequently.

Now all the access to hd_struct->nr_sects should happen using sequence
counter read/update helper functions part_nr_sects_read/part_nr_sects_write.
There is one exception though, set_capacity()/get_capacity(). I think
theoritically race should exist there too but this patch does not
modify set_capacity()/get_capacity() due to sheer number of call sites
and I am afraid that change might break something. I have left that as a
TODO item. We can handle it later if need be. This patch does not introduce
any new races as such w.r.t set_capacity()/get_capacity().

v2: Add CONFIG_LBDAF test to UP preempt case as suggested by Phillip.

Signed-off-by: Vivek Goyal <[email protected]>
Signed-off-by: Phillip Susi <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Vivek Goyal 2012-08-01 12:24:18 +02:00 • committed by Jens Axboe
commit c83f6bf98d
5 changed files with 132 additions and 9 deletions
Download patch file Download diff file Expand all files Collapse all files

59
block/ioctl.c
View file

@ -13,7 +13,7 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
{
struct block_device *bdevp;
struct gendisk *disk;
struct hd_struct *part;
struct hd_struct *part, *lpart;
struct blkpg_ioctl_arg a;
struct blkpg_partition p;
struct disk_part_iter piter;
@ -36,8 +36,8 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
case BLKPG_ADD_PARTITION:
start = p.start >> 9;
length = p.length >> 9;
/* check for fit in a hd_struct */
if (sizeof(sector_t) == sizeof(long) &&
/* check for fit in a hd_struct */
if (sizeof(sector_t) == sizeof(long) &&
sizeof(long long) > sizeof(long)) {
long pstart = start, plength = length;
if (pstart != start || plength != length
@ -91,6 +91,59 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
mutex_unlock(&bdevp->bd_mutex);
bdput(bdevp);
return 0;
case BLKPG_RESIZE_PARTITION:
start = p.start >> 9;
/* new length of partition in bytes */
length = p.length >> 9;
/* check for fit in a hd_struct */
if (sizeof(sector_t) == sizeof(long) &&
sizeof(long long) > sizeof(long)) {
long pstart = start, plength = length;
if (pstart != start || plength != length
|| pstart < 0 || plength < 0)
return -EINVAL;
}
part = disk_get_part(disk, partno);
if (!part)
return -ENXIO;
bdevp = bdget(part_devt(part));
if (!bdevp) {
disk_put_part(part);
return -ENOMEM;
}
mutex_lock(&bdevp->bd_mutex);
mutex_lock_nested(&bdev->bd_mutex, 1);
if (start != part->start_sect) {
mutex_unlock(&bdevp->bd_mutex);
mutex_unlock(&bdev->bd_mutex);
bdput(bdevp);
disk_put_part(part);
return -EINVAL;
}
/* overlap? */
disk_part_iter_init(&piter, disk,
DISK_PITER_INCL_EMPTY);
while ((lpart = disk_part_iter_next(&piter))) {
if (lpart->partno != partno &&
!(start + length <= lpart->start_sect ||
start >= lpart->start_sect + lpart->nr_sects)
) {
disk_part_iter_exit(&piter);
mutex_unlock(&bdevp->bd_mutex);
mutex_unlock(&bdev->bd_mutex);
bdput(bdevp);
disk_put_part(part);
return -EBUSY;
}
}
disk_part_iter_exit(&piter);
part_nr_sects_write(part, (sector_t)length);
i_size_write(bdevp->bd_inode, p.length);
mutex_unlock(&bdevp->bd_mutex);
mutex_unlock(&bdev->bd_mutex);
bdput(bdevp);
disk_put_part(part);
return 0;
default:
return -EINVAL;