iomap: set accurate iter->pos when reading folio ranges

Advance iter to the correct position before calling an IO helper to read
in a folio range. This allows the helper to reliably use iter->pos to
determine the starting offset for reading.

This will simplify the interface for reading in folio ranges when iomap
read/readahead supports caller-provided callbacks.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index f8b17ce549eb60d67174c5cf6e1528dc7b14331f..12b23ff97000d10d4f3228741ed8b70395c9d266 100644 (file)
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -375,10 +375,11 @@ static void iomap_bio_submit_read(struct iomap_read_folio_ctx *ctx)
 }
 
 static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
-               struct iomap_read_folio_ctx *ctx, loff_t pos, size_t plen)
+               struct iomap_read_folio_ctx *ctx, size_t plen)
 {
        struct folio *folio = ctx->cur_folio;
        const struct iomap *iomap = &iter->iomap;
+       loff_t pos = iter->pos;
        size_t poff = offset_in_folio(folio, pos);
        loff_t length = iomap_length(iter);
        sector_t sector;
@@ -506,7 +507,7 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
        loff_t length = iomap_length(iter);
        struct folio *folio = ctx->cur_folio;
        size_t poff, plen;
-       loff_t count;
+       loff_t pos_diff;
        int ret;
 
        if (iomap->type == IOMAP_INLINE) {
@@ -524,12 +525,16 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
                iomap_adjust_read_range(iter->inode, folio, &pos, length, &poff,
                                &plen);
 
-               count = pos - iter->pos + plen;
-               if (WARN_ON_ONCE(count > length))
+               pos_diff = pos - iter->pos;
+               if (WARN_ON_ONCE(pos_diff + plen > length))
                        return -EIO;
 
+               ret = iomap_iter_advance(iter, pos_diff);
+               if (ret)
+                       return ret;
+
                if (plen == 0)
-                       return iomap_iter_advance(iter, count);
+                       return 0;
 
                /* zero post-eof blocks as the page may be mapped */
                if (iomap_block_needs_zeroing(iter, pos)) {
@@ -539,13 +544,13 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
                        if (!*bytes_pending)
                                iomap_read_init(folio);
                        *bytes_pending += plen;
-                       iomap_bio_read_folio_range(iter, ctx, pos, plen);
+                       iomap_bio_read_folio_range(iter, ctx, plen);
                }
 
-               ret = iomap_iter_advance(iter, count);
+               ret = iomap_iter_advance(iter, plen);
                if (ret)
                        return ret;
-               length -= count;
+               length -= pos_diff + plen;
                pos = iter->pos;
        }
        return 0;