filemap: Add fgf_t typedef

Similarly to gfp_t, define fgf_t as its own type to prevent various
misuses and confusion.  Leave the flags as FGP_* for now to reduce the
size of this patch; they will be converted to FGF_* later.  Move the
documentation to the definition of the type insted of burying it in the
__filemap_get_folio() documentation.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/btrfs/file.c

@@ -876,9 +876,9 @@ static int prepare_uptodate_page(struct inode *inode,
 	return 0;
 }
 
-static unsigned int get_prepare_fgp_flags(bool nowait)
+static fgf_t get_prepare_fgp_flags(bool nowait)
 {
-	unsigned int fgp_flags = FGP_LOCK | FGP_ACCESSED | FGP_CREAT;
+	fgf_t fgp_flags = FGP_LOCK | FGP_ACCESSED | FGP_CREAT;
 
 	if (nowait)
 		fgp_flags |= FGP_NOWAIT;
@@ -910,7 +910,7 @@ static noinline int prepare_pages(struct inode *inode, struct page **pages,
 	int i;
 	unsigned long index = pos >> PAGE_SHIFT;
 	gfp_t mask = get_prepare_gfp_flags(inode, nowait);
-	unsigned int fgp_flags = get_prepare_fgp_flags(nowait);
+	fgf_t fgp_flags = get_prepare_fgp_flags(nowait);
 	int err = 0;
 	int faili;
 

fs/f2fs/compress.c

@@ -1045,7 +1045,7 @@ static int prepare_compress_overwrite(struct compress_ctx *cc,
 	struct address_space *mapping = cc->inode->i_mapping;
 	struct page *page;
 	sector_t last_block_in_bio;
-	unsigned fgp_flag = FGP_LOCK | FGP_WRITE | FGP_CREAT;
+	fgf_t fgp_flag = FGP_LOCK | FGP_WRITE | FGP_CREAT;
 	pgoff_t start_idx = start_idx_of_cluster(cc);
 	int i, ret;
 

fs/f2fs/f2fs.h

@@ -2736,7 +2736,7 @@ static inline struct page *f2fs_grab_cache_page(struct address_space *mapping,
 
 static inline struct page *f2fs_pagecache_get_page(
 				struct address_space *mapping, pgoff_t index,
-				int fgp_flags, gfp_t gfp_mask)
+				fgf_t fgp_flags, gfp_t gfp_mask)
 {
 	if (time_to_inject(F2FS_M_SB(mapping), FAULT_PAGE_GET))
 		return NULL;

fs/iomap/buffered-io.c

@@ -467,7 +467,7 @@ EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate);
  */
 struct folio *iomap_get_folio(struct iomap_iter *iter, loff_t pos)
 {
-	unsigned fgp = FGP_WRITEBEGIN | FGP_NOFS;
+	fgf_t fgp = FGP_WRITEBEGIN | FGP_NOFS;
 
 	if (iter->flags & IOMAP_NOWAIT)
 		fgp |= FGP_NOWAIT;

include/linux/pagemap.h

@@ -501,22 +501,48 @@ pgoff_t page_cache_next_miss(struct address_space *mapping,
 pgoff_t page_cache_prev_miss(struct address_space *mapping,
 			     pgoff_t index, unsigned long max_scan);
 
-#define FGP_ACCESSED		0x00000001
-#define FGP_LOCK		0x00000002
-#define FGP_CREAT		0x00000004
-#define FGP_WRITE		0x00000008
-#define FGP_NOFS		0x00000010
-#define FGP_NOWAIT		0x00000020
-#define FGP_FOR_MMAP		0x00000040
-#define FGP_STABLE		0x00000080
+/**
+ * typedef fgf_t - Flags for getting folios from the page cache.
+ *
+ * Most users of the page cache will not need to use these flags;
+ * there are convenience functions such as filemap_get_folio() and
+ * filemap_lock_folio().  For users which need more control over exactly
+ * what is done with the folios, these flags to __filemap_get_folio()
+ * are available.
+ *
+ * * %FGP_ACCESSED - The folio will be marked accessed.
+ * * %FGP_LOCK - The folio is returned locked.
+ * * %FGP_CREAT - If no folio is present then a new folio is allocated,
+ *   added to the page cache and the VM's LRU list.  The folio is
+ *   returned locked.
+ * * %FGP_FOR_MMAP - The caller wants to do its own locking dance if the
+ *   folio is already in cache.  If the folio was allocated, unlock it
+ *   before returning so the caller can do the same dance.
+ * * %FGP_WRITE - The folio will be written to by the caller.
+ * * %FGP_NOFS - __GFP_FS will get cleared in gfp.
+ * * %FGP_NOWAIT - Don't block on the folio lock.
+ * * %FGP_STABLE - Wait for the folio to be stable (finished writeback)
+ * * %FGP_WRITEBEGIN - The flags to use in a filesystem write_begin()
+ *   implementation.
+ */
+typedef unsigned int __bitwise fgf_t;
+
+#define FGP_ACCESSED		((__force fgf_t)0x00000001)
+#define FGP_LOCK		((__force fgf_t)0x00000002)
+#define FGP_CREAT		((__force fgf_t)0x00000004)
+#define FGP_WRITE		((__force fgf_t)0x00000008)
+#define FGP_NOFS		((__force fgf_t)0x00000010)
+#define FGP_NOWAIT		((__force fgf_t)0x00000020)
+#define FGP_FOR_MMAP		((__force fgf_t)0x00000040)
+#define FGP_STABLE		((__force fgf_t)0x00000080)
 
 #define FGP_WRITEBEGIN		(FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)
 
 void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
 struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
-		int fgp_flags, gfp_t gfp);
+		fgf_t fgp_flags, gfp_t gfp);
 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
-		int fgp_flags, gfp_t gfp);
+		fgf_t fgp_flags, gfp_t gfp);
 
 /**
  * filemap_get_folio - Find and get a folio.
@@ -590,7 +616,7 @@ static inline struct page *find_get_page(struct address_space *mapping,
 }
 
 static inline struct page *find_get_page_flags(struct address_space *mapping,
-					pgoff_t offset, int fgp_flags)
+					pgoff_t offset, fgf_t fgp_flags)
 {
 	return pagecache_get_page(mapping, offset, fgp_flags, 0);
 }

mm/filemap.c

@@ -1855,30 +1855,15 @@ out:
  *
  * Looks up the page cache entry at @mapping & @index.
  *
- * @fgp_flags can be zero or more of these flags:
- *
- * * %FGP_ACCESSED - The folio will be marked accessed.
- * * %FGP_LOCK - The folio is returned locked.
- * * %FGP_CREAT - If no page is present then a new page is allocated using
- *   @gfp and added to the page cache and the VM's LRU list.
- *   The page is returned locked and with an increased refcount.
- * * %FGP_FOR_MMAP - The caller wants to do its own locking dance if the
- *   page is already in cache.  If the page was allocated, unlock it before
- *   returning so the caller can do the same dance.
- * * %FGP_WRITE - The page will be written to by the caller.
- * * %FGP_NOFS - __GFP_FS will get cleared in gfp.
- * * %FGP_NOWAIT - Don't get blocked by page lock.
- * * %FGP_STABLE - Wait for the folio to be stable (finished writeback)
- *
  * If %FGP_LOCK or %FGP_CREAT are specified then the function may sleep even
  * if the %GFP flags specified for %FGP_CREAT are atomic.
  *
- * If there is a page cache page, it is returned with an increased refcount.
+ * If this function returns a folio, it is returned with an increased refcount.
  *
  * Return: The found folio or an ERR_PTR() otherwise.
  */
 struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
-		int fgp_flags, gfp_t gfp)
+		fgf_t fgp_flags, gfp_t gfp)
 {
 	struct folio *folio;
 

mm/folio-compat.c

@@ -92,7 +92,7 @@ EXPORT_SYMBOL(add_to_page_cache_lru);
 
 noinline
 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
-		int fgp_flags, gfp_t gfp)
+		fgf_t fgp_flags, gfp_t gfp)
 {
 	struct folio *folio;