mm: return an ERR_PTR from __filemap_get_folio

Instead of returning NULL for all errors, distinguish between:

 - no entry found and not asked to allocated (-ENOENT)
 - failed to allocate memory (-ENOMEM)
 - would block (-EAGAIN)

so that callers don't have to guess the error based on the passed in
flags.

Also pass through the error through the direct callers: filemap_get_folio,
filemap_lock_folio filemap_grab_folio and filemap_get_incore_folio.

[hch@lst.de: fix null-pointer deref]
  Link: https://lkml.kernel.org/r/20230310070023.GA13563@lst.de
  Link: https://lkml.kernel.org/r/20230310043137.GA1624890@u2004
Link: https://lkml.kernel.org/r/20230307143410.28031-8-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Ryusuke Konishi <konishi.ryusuke@gmail.com> [nilfs2]
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 306a0f63cea8..fdcd595d2294 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -520,7 +520,8 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
  * Looks up the page cache entry at @mapping & @index.  If a folio is
  * present, it is returned with an increased refcount.
  *
- * Otherwise, %NULL is returned.
+ * Return: A folio or ERR_PTR(-ENOENT) if there is no folio in the cache for
+ * this index.  Will not return a shadow, swap or DAX entry.
  */
 static inline struct folio *filemap_get_folio(struct address_space *mapping,
 					pgoff_t index)
@@ -537,8 +538,8 @@ static inline struct folio *filemap_get_folio(struct address_space *mapping,
  * present, it is returned locked with an increased refcount.
  *
  * Context: May sleep.
- * Return: A folio or %NULL if there is no folio in the cache for this
- * index.  Will not return a shadow, swap or DAX entry.
+ * Return: A folio or ERR_PTR(-ENOENT) if there is no folio in the cache for
+ * this index.  Will not return a shadow, swap or DAX entry.
  */
 static inline struct folio *filemap_lock_folio(struct address_space *mapping,
 					pgoff_t index)
@@ -555,8 +556,8 @@ static inline struct folio *filemap_lock_folio(struct address_space *mapping,
  * a new folio is created. The folio is locked, marked as accessed, and
  * returned.
  *
- * Return: A found or created folio. NULL if no folio is found and failed to
- * create a folio.
+ * Return: A found or created folio. ERR_PTR(-ENOMEM) if no folio is found
+ * and failed to create a folio.
  */
 static inline struct folio *filemap_grab_folio(struct address_space *mapping,
 					pgoff_t index)