iomap: share iomap_unshare_iter predicate code with fsdax

The predicate code that iomap_unshare_iter uses to decide if it's really
needs to unshare a file range mapping should be shared with the fsdax
version, because right now they're opencoded and inconsistent.

Note that we simplify the predicate logic a bit -- we no longer allow
unsharing of inline data mappings, but there aren't any filesystems that
allow shared inline data currently.

This is a fix in the sense that it should have been ported to fsdax.

Fixes: b53fdb215d13 ("iomap: improve shared block detection in iomap_unshare_iter")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/172796813294.1131942.15762084021076932620.stgit@frogsfrogsfrogs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/dax.c b/fs/dax.c
index c62acd2..5064eef 100644 (file)
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1268,8 +1268,7 @@ static s64 dax_unshare_iter(struct iomap_iter *iter)
        s64 ret = 0;
        void *daddr = NULL, *saddr = NULL;
 
-       /* don't bother with blocks that are not shared to start with */
-       if (!(iomap->flags & IOMAP_F_SHARED))
+       if (!iomap_want_unshare_iter(iter))
                return length;
 
        id = dax_read_lock();

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 78ebd26..3899169 100644 (file)
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1309,19 +1309,12 @@ void iomap_file_buffered_write_punch_delalloc(struct inode *inode,
 }
 EXPORT_SYMBOL_GPL(iomap_file_buffered_write_punch_delalloc);
 
-static loff_t iomap_unshare_iter(struct iomap_iter *iter)
+bool iomap_want_unshare_iter(const struct iomap_iter *iter)
 {
-       struct iomap *iomap = &iter->iomap;
-       loff_t pos = iter->pos;
-       loff_t length = iomap_length(iter);
-       loff_t written = 0;
-
-       /* Don't bother with blocks that are not shared to start with. */
-       if (!(iomap->flags & IOMAP_F_SHARED))
-               return length;
-
        /*
-        * Don't bother with delalloc reservations, holes or unwritten extents.
+        * Don't bother with blocks that are not shared to start with; or
+        * mappings that cannot be shared, such as inline data, delalloc
+        * reservations, holes or unwritten extents.
         *
         * Note that we use srcmap directly instead of iomap_iter_srcmap as
         * unsharing requires providing a separate source map, and the presence
@@ -1329,9 +1322,18 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
         * IOMAP_F_SHARED which can be set for any data that goes into the COW
         * fork for XFS.
         */
-       if (iter->srcmap.type == IOMAP_HOLE ||
-           iter->srcmap.type == IOMAP_DELALLOC ||
-           iter->srcmap.type == IOMAP_UNWRITTEN)
+       return (iter->iomap.flags & IOMAP_F_SHARED) &&
+               iter->srcmap.type == IOMAP_MAPPED;
+}
+
+static loff_t iomap_unshare_iter(struct iomap_iter *iter)
+{
+       struct iomap *iomap = &iter->iomap;
+       loff_t pos = iter->pos;
+       loff_t length = iomap_length(iter);
+       loff_t written = 0;
+
+       if (!iomap_want_unshare_iter(iter))
                return length;
 
        do {

diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 4ad12a3..d8a7fc8 100644 (file)
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -267,6 +267,7 @@ void iomap_invalidate_folio(struct folio *folio, size_t offset, size_t len);
 bool iomap_dirty_folio(struct address_space *mapping, struct folio *folio);
 int iomap_file_unshare(struct inode *inode, loff_t pos, loff_t len,
                const struct iomap_ops *ops);
+bool iomap_want_unshare_iter(const struct iomap_iter *iter);
 int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len,
                bool *did_zero, const struct iomap_ops *ops);
 int iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,