On Fri, Apr 26, 2019 at 03:11:26PM +0200, Andreas Gruenbacher wrote:
> Move the page_done callback into a separate iomap_page_ops structure and
> add a page_prepare calback to be called before the next page is written
> to. In gfs2, we'll want to start a transaction in page_prepare and end
> it in page_done; other filesystems that implement data journaling will
> require the same kind of mechanism.
>
> Signed-off-by: Andreas Gruenbacher <[email protected]>
> ---
> fs/gfs2/bmap.c | 22 +++++++++++++++++-----
> fs/iomap.c | 22 ++++++++++++++++++----
> include/linux/iomap.h | 18 +++++++++++++-----
> 3 files changed, 48 insertions(+), 14 deletions(-)
>
> diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
> index 5da4ca9041c0..6b980703bae7 100644
> --- a/fs/gfs2/bmap.c
> +++ b/fs/gfs2/bmap.c
> @@ -991,15 +991,27 @@ static void gfs2_write_unlock(struct inode *inode)
> gfs2_glock_dq_uninit(&ip->i_gh);
> }
>
> -static void gfs2_iomap_journaled_page_done(struct inode *inode, loff_t pos,
> - unsigned copied, struct page *page,
> - struct iomap *iomap)
> +static int gfs2_iomap_page_prepare(struct inode *inode, loff_t pos,
> + unsigned len, struct iomap *iomap)
> +{
> + return 0;
> +}
> +
> +static void gfs2_iomap_page_done(struct inode *inode, loff_t pos,
> + unsigned copied, struct page *page,
> + struct iomap *iomap)
> {
> struct gfs2_inode *ip = GFS2_I(inode);
>
> - gfs2_page_add_databufs(ip, page, offset_in_page(pos), copied);
> + if (page)
> + gfs2_page_add_databufs(ip, page, offset_in_page(pos), copied);
> }
>
> +static const struct iomap_page_ops gfs2_iomap_page_ops = {
> + .page_prepare = gfs2_iomap_page_prepare,
> + .page_done = gfs2_iomap_page_done,
> +};
> +
> static int gfs2_iomap_begin_write(struct inode *inode, loff_t pos,
> loff_t length, unsigned flags,
> struct iomap *iomap,
> @@ -1077,7 +1089,7 @@ static int gfs2_iomap_begin_write(struct inode *inode,
> loff_t pos,
> }
> }
> if (!gfs2_is_stuffed(ip) && gfs2_is_jdata(ip))
> - iomap->page_done = gfs2_iomap_journaled_page_done;
> + iomap->page_ops = &gfs2_iomap_page_ops;
> return 0;
>
> out_trans_end:
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 3e4652dac9d9..ba2d44b33ed1 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -665,6 +665,7 @@ static int
> iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned
> flags,
> struct page **pagep, struct iomap *iomap)
> {
> + const struct iomap_page_ops *page_ops = iomap->page_ops;
> pgoff_t index = pos >> PAGE_SHIFT;
> struct page *page;
> int status = 0;
> @@ -674,9 +675,17 @@ iomap_write_begin(struct inode *inode, loff_t pos,
> unsigned len, unsigned flags,
> if (fatal_signal_pending(current))
> return -EINTR;
>
> + if (page_ops) {
> + status = page_ops->page_prepare(inode, pos, len, iomap);
> + if (status)
> + return status;
> + }
> +
> page = grab_cache_page_write_begin(inode->i_mapping, index, flags);
> - if (!page)
> - return -ENOMEM;
> + if (!page) {
> + status = -ENOMEM;
> + goto no_page;
> + }
>
> if (iomap->type == IOMAP_INLINE)
> iomap_read_inline_data(inode, page, iomap);
> @@ -684,12 +693,16 @@ iomap_write_begin(struct inode *inode, loff_t pos,
> unsigned len, unsigned flags,
> status = __block_write_begin_int(page, pos, len, NULL, iomap);
> else
> status = __iomap_write_begin(inode, pos, len, page, iomap);
> +
> if (unlikely(status)) {
> unlock_page(page);
> put_page(page);
> page = NULL;
>
> iomap_write_failed(inode, pos, len);
> +no_page:
> + if (page_ops)
> + page_ops->page_done(inode, pos, 0, NULL, iomap);
> }
>
> *pagep = page;
I think we need to clean this area up a bit, this is becoming to
confusing.
Something like:
if (unlikely(status))
goto out_unlock;
*pagep = page;
return 0;
out_unlock:
unlock_page(page);
put_page(page);
iomap_write_failed(inode, pos, len);
out_no_page:
if (page_ops)
page_ops->page_done(inode, pos, 0, NULL, iomap);
*pagep = NULL;
return status;
> + if (page_ops)
> + page_ops->page_done(inode, pos, copied, page, iomap);
Do we always require both pages ops to be set? Wouldn't it be better
to check for the method presence as well?
> +/*
> + * Called before / after processing a page in the mapping returned in this
> + * iomap. At least for now, this is only supported in the buffered write
> path.
> + * When page_prepare returns 0, page_done is called as well
> + * (possibly with page == NULL).
> + */
Not just for now - I think the concept fundamentally only makes sense
for buffered I/O. Maybe we need to express that a little more clearly.
Otherwise looks fine to me.
