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/genhd.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) (limited to 'block/genhd.c') diff --git a/block/genhd.c b/block/genhd.c index 9cf5583c90f..cac7366957c 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -154,7 +154,7 @@ struct hd_struct *disk_part_iter_next(struct disk_part_iter *piter) part = rcu_dereference(ptbl->part[piter->idx]); if (!part) continue; - if (!part->nr_sects && + if (!part_nr_sects_read(part) && !(piter->flags & DISK_PITER_INCL_EMPTY) && !(piter->flags & DISK_PITER_INCL_EMPTY_PART0 && piter->idx == 0)) @@ -191,7 +191,7 @@ EXPORT_SYMBOL_GPL(disk_part_iter_exit); static inline int sector_in_part(struct hd_struct *part, sector_t sector) { return part->start_sect <= sector && - sector < part->start_sect + part->nr_sects; + sector < part->start_sect + part_nr_sects_read(part); } /** @@ -769,8 +769,8 @@ void __init printk_all_partitions(void) printk("%s%s %10llu %s %s", is_part0 ? "" : " ", bdevt_str(part_devt(part), devt_buf), - (unsigned long long)part->nr_sects >> 1, - disk_name(disk, part->partno, name_buf), + (unsigned long long)part_nr_sects_read(part) >> 1 + , disk_name(disk, part->partno, name_buf), uuid_buf); if (is_part0) { if (disk->driverfs_dev != NULL && @@ -862,7 +862,7 @@ static int show_partition(struct seq_file *seqf, void *v) while ((part = disk_part_iter_next(&piter))) seq_printf(seqf, "%4d %7d %10llu %s\n", MAJOR(part_devt(part)), MINOR(part_devt(part)), - (unsigned long long)part->nr_sects >> 1, + (unsigned long long)part_nr_sects_read(part) >> 1, disk_name(sgp, part->partno, buf)); disk_part_iter_exit(&piter); @@ -1268,6 +1268,16 @@ struct gendisk *alloc_disk_node(int minors, int node_id) } disk->part_tbl->part[0] = &disk->part0; + /* + * set_capacity() and get_capacity() currently don't use + * seqcounter to read/update the part0->nr_sects. Still init + * the counter as we can read the sectors in IO submission + * patch using seqence counters. + * + * TODO: Ideally set_capacity() and get_capacity() should be + * converted to make use of bd_mutex and sequence counters. + */ + seqcount_init(&disk->part0.nr_sects_seq); hd_ref_init(&disk->part0); disk->minors = minors; -- cgit v1.2.3