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Re: [dm-devel] [PATCH 1/2] block: add partition resize function to blkpg ioctl



On Tue, Feb 14, 2012 at 03:39:50PM -0500, Vivek Goyal wrote:
> 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.
> 
> Signed-off-by: Vivek Goyal <vgoyal redhat com>

Hi Jens,

Can you please consider this patch for inclusion. One of our customer
does want to be able to grow partitions without having to reboot
the system.

Thanks
Vivek

> ---
>  block/genhd.c             |   20 ++++++++++++----
>  block/ioctl.c             |   57 ++++++++++++++++++++++++++++++++++++++++++--
>  block/partition-generic.c |    4 ++-
>  include/linux/blkpg.h     |    1 +
>  include/linux/genhd.h     |   57 +++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 130 insertions(+), 9 deletions(-)
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index 23b4f70..935e09b 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -153,7 +153,7 @@ 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))
> @@ -190,7 +190,7 @@ 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);
>  }
>  
>  /**
> @@ -765,8 +765,8 @@ 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), uuid);
> +			       (unsigned long long)part_nr_sects_read(part) >> 1
> +			       , disk_name(disk, part->partno, name_buf), uuid);
>  			if (is_part0) {
>  				if (disk->driverfs_dev != NULL &&
>  				    disk->driverfs_dev->driver != NULL)
> @@ -857,7 +857,7 @@ 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);
>  
> @@ -1263,6 +1263,16 @@ 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;
> diff --git a/block/ioctl.c b/block/ioctl.c
> index ba15b2d..ddbc649 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -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
> @@ -92,6 +92,57 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
>  			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);
> +				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);
> +					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;
>  	}
> diff --git a/block/partition-generic.c b/block/partition-generic.c
> index d06ec1c..363a6f6 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;
> diff --git a/include/linux/blkpg.h b/include/linux/blkpg.h
> index faf8a45..a851944 100644
> --- a/include/linux/blkpg.h
> +++ b/include/linux/blkpg.h
> @@ -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
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index fe23ee7..0def3ef 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -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;
> @@ -653,6 +659,57 @@ 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_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) { }
> -- 
> 1.7.6.4


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