From c83f6bf98dc1f1a194118b3830706cebbebda8c4 Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Wed, 1 Aug 2012 12:24:18 +0200 Subject: 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 Signed-off-by: Phillip Susi Signed-off-by: Jens Axboe --- block/partition-generic.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'block/partition-generic.c') diff --git a/block/partition-generic.c b/block/partition-generic.c index 6df5d6928a440..f1d14519cc040 100644 --- a/block/partition-generic.c +++ b/block/partition-generic.c @@ -84,7 +84,7 @@ ssize_t part_size_show(struct device *dev, 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 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno, err = -ENOMEM; goto out_free; } + + seqcount_init(&p->nr_sects_seq); pdev = part_to_dev(p); p->start_sect = start; -- cgit v1.2.3