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



On Mon, Feb 20, 2012 at 10:28:49AM -0500, Vivek Goyal wrote:
> 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.

Hi Jens,

Do you have concerns about this patch? If no, can you please consider
merging it.

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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