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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>
This commit is contained in:
Vivek Goyal 2012-08-01 12:24:18 +02:00 committed by Jens Axboe
parent 4638a83e86
commit c83f6bf98d
5 changed files with 132 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
block/genhd.c
View File

@ -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;

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;

4
block/partition-generic.c
View File

@ -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;

1
include/linux/blkpg.h
View File

@ -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

57
include/linux/genhd.h
View File

@ -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) { }