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Date: Tue, 17 Nov 2015 20:38:04 -0800
From: "Darrick J. Wong" <darrick.wong@...cle.com>
To: Jeff Moyer <jmoyer@...hat.com>
Cc: Jens Axboe <axboe@...nel.dk>,
Christoph Hellwig <hch@...radead.org>,
"Seymour, Shane M" <shane.seymour@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
Jeff Layton <jlayton@...chiereds.net>,
"J. Bruce Fields" <bfields@...ldses.org>,
"martin.petersen@...cle.com" <martin.petersen@...cle.com>
Subject: Re: [PATCH v3] block: create ioctl to discard-or-zeroout a range of
blocks
On Fri, Nov 13, 2015 at 03:23:25PM -0500, Jeff Moyer wrote:
> "Darrick J. Wong" <darrick.wong@...cle.com> writes:
>
> > Create a new ioctl to expose the block layer's newfound ability to
> > issue either a zeroing discard, a WRITE SAME with a zero page, or a
> > regular write with the zero page. This BLKZEROOUT2 ioctl takes
> > {start, length, flags} as parameters. So far, the only flag available
> > is to enable the zeroing discard part -- without it, the call invokes
> > the old BLKZEROOUT behavior. start and length have the same meaning
> > as in BLKZEROOUT.
> >
> > Furthermore, because BLKZEROOUT2 issues commands directly to the
> > storage device, we must invalidate the page cache (as a regular
> > O_DIRECT write would do) to avoid returning stale cache contents at a
> > later time.
> >
> > v3: Add extra padding for future expansion, and check the padding is zero.
>
> Is there someplace we document ioctls? This stuff really could use some
> good documentation.
There's no place that I know of. I looked in man-pages.git but didn't see
anything promising. There's what, like ~2000 ioctls?
--D
>
> Cheers,
> Jeff
>
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> > ---
> > block/ioctl.c | 48 ++++++++++++++++++++++++++++++++++++++++-------
> > include/uapi/linux/fs.h | 9 +++++++++
> > 2 files changed, 50 insertions(+), 7 deletions(-)
> >
> > diff --git a/block/ioctl.c b/block/ioctl.c
> > index 8061eba..8e67551 100644
> > --- a/block/ioctl.c
> > +++ b/block/ioctl.c
> > @@ -213,19 +213,39 @@ static int blk_ioctl_discard(struct block_device *bdev, uint64_t start,
> > }
> >
> > static int blk_ioctl_zeroout(struct block_device *bdev, uint64_t start,
> > - uint64_t len)
> > + uint64_t len, uint32_t flags)
> > {
> > + int ret;
> > + struct address_space *mapping;
> > + uint64_t end = start + len - 1;
> > +
> > + if (flags & ~BLKZEROOUT2_DISCARD_OK)
> > + return -EINVAL;
> > if (start & 511)
> > return -EINVAL;
> > if (len & 511)
> > return -EINVAL;
> > - start >>= 9;
> > - len >>= 9;
> > -
> > - if (start + len > (i_size_read(bdev->bd_inode) >> 9))
> > + if (end >= i_size_read(bdev->bd_inode))
> > return -EINVAL;
> >
> > - return blkdev_issue_zeroout(bdev, start, len, GFP_KERNEL, false);
> > + /* Invalidate the page cache, including dirty pages */
> > + mapping = bdev->bd_inode->i_mapping;
> > + truncate_inode_pages_range(mapping, start, end);
> > +
> > + ret = blkdev_issue_zeroout(bdev, start >> 9, len >> 9, GFP_KERNEL,
> > + flags & BLKZEROOUT2_DISCARD_OK);
> > + if (ret)
> > + goto out;
> > +
> > + /*
> > + * Invalidate again; if someone wandered in and dirtied a page,
> > + * the caller will be given -EBUSY.
> > + */
> > + ret = invalidate_inode_pages2_range(mapping,
> > + start >> PAGE_CACHE_SHIFT,
> > + end >> PAGE_CACHE_SHIFT);
> > +out:
> > + return ret;
> > }
> >
> > static int put_ushort(unsigned long arg, unsigned short val)
> > @@ -353,7 +373,21 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
> > if (copy_from_user(range, (void __user *)arg, sizeof(range)))
> > return -EFAULT;
> >
> > - return blk_ioctl_zeroout(bdev, range[0], range[1]);
> > + return blk_ioctl_zeroout(bdev, range[0], range[1], 0);
> > + }
> > + case BLKZEROOUT2: {
> > + struct blkzeroout2 p;
> > +
> > + if (!(mode & FMODE_WRITE))
> > + return -EBADF;
> > +
> > + if (copy_from_user(&p, (void __user *)arg, sizeof(p)))
> > + return -EFAULT;
> > +
> > + if (p.padding || p.padding2)
> > + return -EINVAL;
> > +
> > + return blk_ioctl_zeroout(bdev, p.start, p.length, p.flags);
> > }
> >
> > case HDIO_GETGEO: {
> > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> > index 9b964a5..b811fa4 100644
> > --- a/include/uapi/linux/fs.h
> > +++ b/include/uapi/linux/fs.h
> > @@ -152,6 +152,15 @@ struct inodes_stat_t {
> > #define BLKSECDISCARD _IO(0x12,125)
> > #define BLKROTATIONAL _IO(0x12,126)
> > #define BLKZEROOUT _IO(0x12,127)
> > +struct blkzeroout2 {
> > + __u64 start;
> > + __u64 length;
> > + __u32 flags;
> > + __u32 padding;
> > + __u64 padding2;
> > +};
> > +#define BLKZEROOUT2_DISCARD_OK 1
> > +#define BLKZEROOUT2 _IOR(0x12, 127, struct blkzeroout2)
> >
> > #define BMAP_IOCTL 1 /* obsolete - kept for compatibility */
> > #define FIBMAP _IO(0x00,1) /* bmap access */
> > --
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