block: add partition resize function to blkpg ioctl
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 <vgoyal@redhat.com>
Signed-off-by: Phillip Susi <psusi@ubuntu.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/partition-generic.c b/block/partition-generic.c
index 6df5d69..f1d1451 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -84,7 +84,7 @@
struct device_attribute *attr, char *buf)
{
struct hd_struct *p = dev_to_part(dev);
- return sprintf(buf, "%llu\n",(unsigned long long)p->nr_sects);
+ return sprintf(buf, "%llu\n",(unsigned long long)part_nr_sects_read(p));
}
static ssize_t part_ro_show(struct device *dev,
@@ -294,6 +294,8 @@
err = -ENOMEM;
goto out_free;
}
+
+ seqcount_init(&p->nr_sects_seq);
pdev = part_to_dev(p);
p->start_sect = start;