mm: add folio_end_read()

Provide a function for filesystems to call when they have finished reading
an entire folio.

Link: https://lkml.kernel.org/r/20231004165317.1061855-4-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/pagemap.h

@@ -1101,6 +1101,7 @@ static inline void wait_on_page_locked(struct page *page)
 	folio_wait_locked(page_folio(page));
 }
 
+void folio_end_read(struct folio *folio, bool success);
 void wait_on_page_writeback(struct page *page);
 void folio_wait_writeback(struct folio *folio);
 int folio_wait_writeback_killable(struct folio *folio);

mm/filemap.c

@@ -1525,6 +1525,28 @@ void folio_unlock(struct folio *folio)
 }
 EXPORT_SYMBOL(folio_unlock);
 
+/**
+ * folio_end_read - End read on a folio.
+ * @folio: The folio.
+ * @success: True if all reads completed successfully.
+ *
+ * When all reads against a folio have completed, filesystems should
+ * call this function to let the pagecache know that no more reads
+ * are outstanding.  This will unlock the folio and wake up any thread
+ * sleeping on the lock.  The folio will also be marked uptodate if all
+ * reads succeeded.
+ *
+ * Context: May be called from interrupt or process context.  May not be
+ * called from NMI context.
+ */
+void folio_end_read(struct folio *folio, bool success)
+{
+	if (likely(success))
+		folio_mark_uptodate(folio);
+	folio_unlock(folio);
+}
+EXPORT_SYMBOL(folio_end_read);
+
 /**
  * folio_end_private_2 - Clear PG_private_2 and wake any waiters.
  * @folio: The folio.