Re: [dm-devel] [RFC PATCH v4 2/3] block: add simple copy support

[Darrick J. Wong]

SelvaKumar S: This didn't show up on dm-devel, sorry for the OT reply...

On Mon, Jan 04, 2021 at 12:47:11PM +0000, Damien Le Moal wrote:
> On 2021/01/04 19:48, SelvaKumar S wrote:
> > Add new BLKCOPY ioctl that offloads copying of one or more sources
> > ranges to a destination in the device. Accepts copy_ranges that contains
> > destination, no of sources and pointer to the array of source
> > ranges. Each range_entry contains start and length of source
> > ranges (in bytes).
> > 
> > Introduce REQ_OP_COPY, a no-merge copy offload operation. Create
> > bio with control information as payload and submit to the device.
> > REQ_OP_COPY(19) is a write op and takes zone_write_lock when submitted
> > to zoned device.
> > 
> > If the device doesn't support copy or copy offload is disabled, then
> > copy is emulated by allocating memory of total copy size. The source
> > ranges are read into memory by chaining bio for each source ranges and
> > submitting them async and the last bio waits for completion. After data
> > is read, it is written to the destination.
> > 
> > bio_map_kern() is used to allocate bio and add pages of copy buffer to
> > bio. As bio->bi_private and bio->bi_end_io is needed for chaining the
> > bio and over written, invalidate_kernel_vmap_range() for read is called
> > in the caller.
> > 
> > Introduce queue limits for simple copy and other helper functions.
> > Add device limits as sysfs entries.
> > 	- copy_offload
> > 	- max_copy_sectors
> > 	- max_copy_ranges_sectors
> > 	- max_copy_nr_ranges
> > 
> > copy_offload(= 0) is disabled by default.
> > max_copy_sectors = 0 indicates the device doesn't support native copy.
> > 
> > Native copy offload is not supported for stacked devices and is done via
> > copy emulation.
> > 
> > Signed-off-by: SelvaKumar S <selvakuma.s1@xxxxxxxxxxx>
> > Signed-off-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
> > Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
> > Signed-off-by: Javier González <javier.gonz@xxxxxxxxxxx>
> > ---
> >  block/blk-core.c          |  94 ++++++++++++++--
> >  block/blk-lib.c           | 223 ++++++++++++++++++++++++++++++++++++++
> >  block/blk-merge.c         |   2 +
> >  block/blk-settings.c      |  10 ++
> >  block/blk-sysfs.c         |  50 +++++++++
> >  block/blk-zoned.c         |   1 +
> >  block/bounce.c            |   1 +
> >  block/ioctl.c             |  43 ++++++++
> >  include/linux/bio.h       |   1 +
> >  include/linux/blk_types.h |  15 +++
> >  include/linux/blkdev.h    |  13 +++
> >  include/uapi/linux/fs.h   |  13 +++

This series should also be cc'd to linux-api since you're adding a new
userspace api.

Alternately, save yourself the trouble of passing userspace API review
by hooking this up to the existing copy_file_range call in the vfs.  /me
hopes you sent blktests to check the operation of this thing, since none
of the original patches made it to this list.

If you really /do/ need a new kernel call for this, then please send in
a manpage documenting the fields of struct range_entry and copy_range,
and how users are supposed to use this.

<now jumping to the ioctl definition because Damien already reviewed the
plumbing...>

> > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> > index f44eb0a04afd..5cadb176317a 100644
> > --- a/include/uapi/linux/fs.h
> > +++ b/include/uapi/linux/fs.h
> > @@ -64,6 +64,18 @@ struct fstrim_range {
> >  	__u64 minlen;
> >  };
> >  
> > +struct range_entry {
> > +	__u64 src;

Is this an offset?  Or the fd of an open bdev?

> > +	__u64 len;
> > +};
> > +
> > +struct copy_range {
> > +	__u64 dest;
> > +	__u64 nr_range;
> > +	__u64 range_list;

Hm, I think this is a pointer?  Why not just put the range_entry array
at the end of struct copy_range?

> > +	__u64 rsvd;

Also needs a flags argument so we don't have to add BLKCOPY2 in like 3
months.

--D

> > +};
> > +
> >  /* extent-same (dedupe) ioctls; these MUST match the btrfs ioctl definitions */
> >  #define FILE_DEDUPE_RANGE_SAME		0
> >  #define FILE_DEDUPE_RANGE_DIFFERS	1
> > @@ -184,6 +196,7 @@ struct fsxattr {
> >  #define BLKSECDISCARD _IO(0x12,125)
> >  #define BLKROTATIONAL _IO(0x12,126)
> >  #define BLKZEROOUT _IO(0x12,127)
> > +#define BLKCOPY _IOWR(0x12, 128, struct copy_range)
> >  /*
> >   * A jump here: 130-131 are reserved for zoned block devices
> >   * (see uapi/linux/blkzoned.h)
> > 
> 
> 
> -- 
> Damien Le Moal
> Western Digital Research
> 
> 
> 
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