erofs/zmap.c: Fix incorrect offset calculation

[platform/kernel/linux-starfive.git] / fs / erofs / zmap.c

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index e6d5d7a..39cc014 100644 (file)
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -793,12 +793,16 @@ static int z_erofs_iomap_begin_report(struct inode *inode, loff_t offset,
                iomap->type = IOMAP_HOLE;
                iomap->addr = IOMAP_NULL_ADDR;
                /*
-                * No strict rule how to describe extents for post EOF, yet
-                * we need do like below. Otherwise, iomap itself will get
+                * No strict rule on how to describe extents for post EOF, yet
+                * we need to do like below. Otherwise, iomap itself will get
                 * into an endless loop on post EOF.
+                *
+                * Calculate the effective offset by subtracting extent start
+                * (map.m_la) from the requested offset, and add it to length.
+                * (NB: offset >= map.m_la always)
                 */
                if (iomap->offset >= inode->i_size)
-                       iomap->length = length + map.m_la - offset;
+                       iomap->length = length + offset - map.m_la;
        }
        iomap->flags = 0;
        return 0;