linux-ext4 - Re: [PATCH 4/6] vfs: Add iomap_seek_hole and iomap_seek

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Date:   Wed, 28 Jun 2017 00:14:57 +0200
From:   Andreas Grünbacher <andreas.gruenbacher@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Andreas Gruenbacher <agruenba@...hat.com>, Jan Kara <jack@...e.cz>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/6] vfs: Add iomap_seek_hole and iomap_seek_data helpers

2017-06-27 23:48 GMT+02:00 Christoph Hellwig <hch@....de>:
> From: Andreas Gruenbacher <agruenba@...hat.com>
>
> Filesystems can use this for implementing lseek SEEK_HOLE / SEEK_DATA
> support via iomap.
>
> Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
> [hch: split functions, coding style cleanups]
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  fs/iomap.c            | 98 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/iomap.h |  4 +++
>  2 files changed, 102 insertions(+)
>
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 4b10892967a5..c90cda33994b 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -584,6 +584,104 @@ int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fi,
>  }
>  EXPORT_SYMBOL_GPL(iomap_fiemap);
>
> +static loff_t
> +iomap_seek_hole_actor(struct inode *inode, loff_t offset, loff_t length,
> +                     void *data, struct iomap *iomap)
> +{
> +       switch (iomap->type) {
> +       case IOMAP_UNWRITTEN:
> +               offset = page_cache_seek_hole_data(inode, offset, length,
> +                                                  SEEK_HOLE);
> +               if (offset < 0)
> +                       return length;
> +               /* fall through */
> +       case IOMAP_HOLE:
> +               *(loff_t *)data = offset;
> +               return 0;
> +       default:
> +               return length;
> +       }
> +}
> +
> +loff_t
> +iomap_seek_hole(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
> +{
> +       loff_t size = i_size_read(inode);
> +       loff_t length = size - offset;
> +       loff_t ret;
> +
> +       /* Nothing to be found beyond the end of the file. */
> +       if (offset >= size)
> +               return -ENXIO;
> +
> +       while (length > 0) {
> +               ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
> +                                 &offset, iomap_seek_hole_actor);
> +               if (ret < 0)
> +                       return ret;
> +               if (ret == 0)
> +                       break;
> +
> +               offset += ret;
> +               length -= ret;
> +       }
> +
> +       /* The last segment can extend beyond the end of the file. */
> +       if (length <= 0)
> +               return min(offset, size);

This shouldn't be true anymore now that the actors don't recompute the
length; the above three lines should be obsolete.

> +       return offset;
> +}
> +EXPORT_SYMBOL_GPL(iomap_seek_hole);
> +
> +static loff_t
> +iomap_seek_data_actor(struct inode *inode, loff_t offset, loff_t length,
> +                     void *data, struct iomap *iomap)
> +{
> +       switch (iomap->type) {
> +       case IOMAP_HOLE:
> +               return length;
> +       case IOMAP_UNWRITTEN:
> +               offset = page_cache_seek_hole_data(inode, offset, length,
> +                                                  SEEK_DATA);
> +               if (offset < 0)
> +                       return length;
> +               /*FALLTHRU*/
> +       default:
> +               *(loff_t *)data = offset;
> +               return 0;
> +       }
> +}
> +
> +loff_t
> +iomap_seek_data(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
> +{
> +       loff_t size = i_size_read(inode);
> +       loff_t length = size - offset;
> +       loff_t ret;
> +
> +       /* Nothing to be found beyond the end of the file. */
> +       if (offset >= size)
> +               return -ENXIO;
> +
> +       while (length > 0) {
> +               ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
> +                                 &offset, iomap_seek_data_actor);
> +               if (ret < 0)
> +                       return ret;
> +               if (ret == 0)
> +                       break;
> +
> +               offset += ret;
> +               length -= ret;
> +       }
> +
> +       /* There is an implicit hole at the end of the file. */

This comment makes more sense in iomap_seek_hole now.

> +       if (length <= 0)
> +               return -ENXIO;
> +       return offset;
> +}
> +EXPORT_SYMBOL_GPL(iomap_seek_data);
> +
>  /*
>   * Private flags for iomap_dio, must not overlap with the public ones in
>   * iomap.h:
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index f753e788da31..8a03f5dcd89b 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -83,6 +83,10 @@ int iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
>  int iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops);
>  int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>                 loff_t start, loff_t len, const struct iomap_ops *ops);
> +loff_t iomap_seek_hole(struct inode *inode, loff_t offset,
> +               const struct iomap_ops *ops);
> +loff_t iomap_seek_data(struct inode *inode, loff_t offset,
> +               const struct iomap_ops *ops);
>
>  /*
>   * Flags for direct I/O ->end_io:
> --
> 2.11.0

Thanks,
Andreas