Commit c83f6bf9 authored by Vivek Goyal's avatar Vivek Goyal Committed by Jens Axboe
Browse files

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: default avatarVivek Goyal <vgoyal@redhat.com>
Signed-off-by: default avatarPhillip Susi <psusi@ubuntu.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 4638a83e

block/genhd.c

+15 −5
Original line number Diff line number Diff line
@@ -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;

block/ioctl.c

+56 −3
Original line number Diff line number Diff line
@@ -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;
@@ -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;

block/partition-generic.c

+3 −1
Original line number Diff line number Diff line
@@ -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;

include/linux/blkpg.h

+1 −0
Original line number Diff line number Diff line
@@ -40,6 +40,7 @@ struct blkpg_ioctl_arg { 
/* The subfunctions (for the op field) */

#define BLKPG_ADD_PARTITION	1

#define BLKPG_DEL_PARTITION	2

#define BLKPG_RESIZE_PARTITION	3



/* Sizes of name fields. Unused at present. */

#define BLKPG_DEVNAMELTH	64

include/linux/genhd.h

+57 −0
Original line number Diff line number Diff line
@@ -98,7 +98,13 @@ struct partition_meta_info { 


struct hd_struct {

	sector_t start_sect;

	/*

	 * nr_sects is protected by sequence counter. 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.

	 */

	sector_t nr_sects;

	seqcount_t nr_sects_seq;

	sector_t alignment_offset;

	unsigned int discard_alignment;

	struct device __dev;
@@ -648,6 +654,57 @@ static inline void hd_struct_put(struct hd_struct *part) 
		__delete_partition(part);

}



/*

 * Any access of part->nr_sects which is not protected by partition

 * bd_mutex or gendisk bdev bd_mutex, should be done using this

 * accessor function.

 *

 * Code written along the lines of i_size_read() and i_size_write().

 * CONFIG_PREEMPT case optimizes the case of UP kernel with preemption

 * on.

 */

static inline sector_t part_nr_sects_read(struct hd_struct *part)

{

#if BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_SMP)

	sector_t nr_sects;

	unsigned seq;

	do {

		seq = read_seqcount_begin(&part->nr_sects_seq);

		nr_sects = part->nr_sects;

	} while (read_seqcount_retry(&part->nr_sects_seq, seq));

	return nr_sects;

#elif BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_PREEMPT)

	sector_t nr_sects;



	preempt_disable();

	nr_sects = part->nr_sects;

	preempt_enable();

	return nr_sects;

#else

	return part->nr_sects;

#endif

}



/*

 * Should be called with mutex lock held (typically bd_mutex) of partition

 * to provide mutual exlusion among writers otherwise seqcount might be

 * left in wrong state leaving the readers spinning infinitely.

 */

static inline void part_nr_sects_write(struct hd_struct *part, sector_t size)

{

#if BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_SMP)

	write_seqcount_begin(&part->nr_sects_seq);

	part->nr_sects = size;

	write_seqcount_end(&part->nr_sects_seq);

#elif BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_PREEMPT)

	preempt_disable();

	part->nr_sects = size;

	preempt_enable();

#else

	part->nr_sects = size;

#endif

}



#else /* CONFIG_BLOCK */



static inline void printk_all_partitions(void) { }

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