| Message ID | 20250205135821.178256-8-bfoster@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | iomap: incremental per-operation iter advance | expand |
On Wed, Feb 05, 2025 at 08:58:18AM -0500, Brian Foster wrote: > The current iomap_iter iteration model reads the mapping from the > filesystem, processes the subrange of the operation associated with > the current mapping, and returns the number of bytes processed back > to the iteration code. The latter advances the position and > remaining length of the iter in preparation for the next iteration. > > At the _iter() handler level, this tends to produce a processing > loop where the local code pulls the current position and remaining > length out of the iter, iterates it locally based on file offset, > and then breaks out when the associated range has been fully > processed. > > This works well enough for current handlers, but upcoming > enhancements require a bit more flexibility in certain situations. > Enhancements for zero range will lead to a situation where the > processing loop is no longer a pure ascending offset walk, but > rather dictated by pagecache state and folio lookup. Since folio > lookup and write preparation occur at different levels, it is more > difficult to manage position and length outside of the iter. > > To provide more flexibility to certain iomap operations, introduce > support for incremental iomap_iter advances from within the > operation itself. This allows more granular advances for operations > that might not use the typical file offset based walk. > > Note that the semantics for operations that use incremental advances > is slightly different than traditional operations. Operations that > advance the iter directly are expected to return success or failure > (i.e. 0 or negative error code) in iter.processed rather than the > number of bytes processed. I think this needs to be documented in the code comments for @processed in iomap.h: * @processed: The iteration loop body should set this to a negative * errno if an error occurs during processing; zero if it advanced * the iter itself with iomap_iter_advance; or the number of bytes * processed if it needs iomap_iter to advance the iter. --D > Signed-off-by: Brian Foster <bfoster@redhat.com> > Reviewed-by: Christoph Hellwig <hch@lst.de> > --- > fs/iomap/iter.c | 32 +++++++++++++++++++++++++------- > include/linux/iomap.h | 3 +++ > 2 files changed, 28 insertions(+), 7 deletions(-) > > diff --git a/fs/iomap/iter.c b/fs/iomap/iter.c > index cdba24dbbfd7..9273ef36d5ae 100644 > --- a/fs/iomap/iter.c > +++ b/fs/iomap/iter.c > @@ -35,6 +35,8 @@ static inline void iomap_iter_done(struct iomap_iter *iter) > WARN_ON_ONCE(iter->iomap.offset + iter->iomap.length <= iter->pos); > WARN_ON_ONCE(iter->iomap.flags & IOMAP_F_STALE); > > + iter->iter_start_pos = iter->pos; > + > trace_iomap_iter_dstmap(iter->inode, &iter->iomap); > if (iter->srcmap.type != IOMAP_HOLE) > trace_iomap_iter_srcmap(iter->inode, &iter->srcmap); > @@ -58,6 +60,8 @@ static inline void iomap_iter_done(struct iomap_iter *iter) > int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) > { > bool stale = iter->iomap.flags & IOMAP_F_STALE; > + ssize_t advanced = iter->processed > 0 ? iter->processed : 0; > + u64 olen = iter->len; > s64 processed; > int ret; > > @@ -66,11 +70,22 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) > if (!iter->iomap.length) > goto begin; > > + /* > + * If iter.processed is zero, the op may still have advanced the iter > + * itself. Calculate the advanced and original length bytes based on how > + * far pos has advanced for ->iomap_end(). > + */ > + if (!advanced) { > + advanced = iter->pos - iter->iter_start_pos; > + olen += advanced; > + } > + > if (ops->iomap_end) { > - ret = ops->iomap_end(iter->inode, iter->pos, iomap_length(iter), > - iter->processed > 0 ? iter->processed : 0, > - iter->flags, &iter->iomap); > - if (ret < 0 && !iter->processed) > + ret = ops->iomap_end(iter->inode, iter->iter_start_pos, > + iomap_length_trim(iter, iter->iter_start_pos, > + olen), > + advanced, iter->flags, &iter->iomap); > + if (ret < 0 && !advanced) > return ret; > } > > @@ -81,8 +96,11 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) > } > > /* > - * Advance the iter and clear state from the previous iteration. Use > - * iter->len to determine whether to continue onto the next mapping. > + * Advance the iter and clear state from the previous iteration. This > + * passes iter->processed because that reflects the bytes processed but > + * not yet advanced by the iter handler. > + * > + * Use iter->len to determine whether to continue onto the next mapping. > * Explicitly terminate in the case where the current iter has not > * advanced at all (i.e. no work was done for some reason) unless the > * mapping has been marked stale and needs to be reprocessed. > @@ -90,7 +108,7 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) > ret = iomap_iter_advance(iter, &processed); > if (!ret && iter->len > 0) > ret = 1; > - if (ret > 0 && !iter->processed && !stale) > + if (ret > 0 && !advanced && !stale) > ret = 0; > iomap_iter_reset_iomap(iter); > if (ret <= 0) > diff --git a/include/linux/iomap.h b/include/linux/iomap.h > index f304c602e5fe..0135a7f8dd83 100644 > --- a/include/linux/iomap.h > +++ b/include/linux/iomap.h > @@ -211,6 +211,8 @@ struct iomap_ops { > * calls to iomap_iter(). Treat as read-only in the body. > * @len: The remaining length of the file segment we're operating on. > * It is updated at the same time as @pos. > + * @iter_start_pos: The original start pos for the current iomap. Used for > + * incremental iter advance. > * @processed: The number of bytes processed by the body in the most recent > * iteration, or a negative errno. 0 causes the iteration to stop. > * @flags: Zero or more of the iomap_begin flags above. > @@ -221,6 +223,7 @@ struct iomap_iter { > struct inode *inode; > loff_t pos; > u64 len; > + loff_t iter_start_pos; > s64 processed; > unsigned flags; > struct iomap iomap; > -- > 2.48.1 > >
diff --git a/fs/iomap/iter.c b/fs/iomap/iter.c index cdba24dbbfd7..9273ef36d5ae 100644 --- a/fs/iomap/iter.c +++ b/fs/iomap/iter.c @@ -35,6 +35,8 @@ static inline void iomap_iter_done(struct iomap_iter *iter) WARN_ON_ONCE(iter->iomap.offset + iter->iomap.length <= iter->pos); WARN_ON_ONCE(iter->iomap.flags & IOMAP_F_STALE); + iter->iter_start_pos = iter->pos; + trace_iomap_iter_dstmap(iter->inode, &iter->iomap); if (iter->srcmap.type != IOMAP_HOLE) trace_iomap_iter_srcmap(iter->inode, &iter->srcmap); @@ -58,6 +60,8 @@ static inline void iomap_iter_done(struct iomap_iter *iter) int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) { bool stale = iter->iomap.flags & IOMAP_F_STALE; + ssize_t advanced = iter->processed > 0 ? iter->processed : 0; + u64 olen = iter->len; s64 processed; int ret; @@ -66,11 +70,22 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) if (!iter->iomap.length) goto begin; + /* + * If iter.processed is zero, the op may still have advanced the iter + * itself. Calculate the advanced and original length bytes based on how + * far pos has advanced for ->iomap_end(). + */ + if (!advanced) { + advanced = iter->pos - iter->iter_start_pos; + olen += advanced; + } + if (ops->iomap_end) { - ret = ops->iomap_end(iter->inode, iter->pos, iomap_length(iter), - iter->processed > 0 ? iter->processed : 0, - iter->flags, &iter->iomap); - if (ret < 0 && !iter->processed) + ret = ops->iomap_end(iter->inode, iter->iter_start_pos, + iomap_length_trim(iter, iter->iter_start_pos, + olen), + advanced, iter->flags, &iter->iomap); + if (ret < 0 && !advanced) return ret; } @@ -81,8 +96,11 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) } /* - * Advance the iter and clear state from the previous iteration. Use - * iter->len to determine whether to continue onto the next mapping. + * Advance the iter and clear state from the previous iteration. This + * passes iter->processed because that reflects the bytes processed but + * not yet advanced by the iter handler. + * + * Use iter->len to determine whether to continue onto the next mapping. * Explicitly terminate in the case where the current iter has not * advanced at all (i.e. no work was done for some reason) unless the * mapping has been marked stale and needs to be reprocessed. @@ -90,7 +108,7 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops) ret = iomap_iter_advance(iter, &processed); if (!ret && iter->len > 0) ret = 1; - if (ret > 0 && !iter->processed && !stale) + if (ret > 0 && !advanced && !stale) ret = 0; iomap_iter_reset_iomap(iter); if (ret <= 0) diff --git a/include/linux/iomap.h b/include/linux/iomap.h index f304c602e5fe..0135a7f8dd83 100644 --- a/include/linux/iomap.h +++ b/include/linux/iomap.h @@ -211,6 +211,8 @@ struct iomap_ops { * calls to iomap_iter(). Treat as read-only in the body. * @len: The remaining length of the file segment we're operating on. * It is updated at the same time as @pos. + * @iter_start_pos: The original start pos for the current iomap. Used for + * incremental iter advance. * @processed: The number of bytes processed by the body in the most recent * iteration, or a negative errno. 0 causes the iteration to stop. * @flags: Zero or more of the iomap_begin flags above. @@ -221,6 +223,7 @@ struct iomap_iter { struct inode *inode; loff_t pos; u64 len; + loff_t iter_start_pos; s64 processed; unsigned flags; struct iomap iomap;