fuse: support large folios for retrieves

Add support for folios larger than one page size for retrieves.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Bernd Schubert <bschubert@ddn.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Author: joannekoong

fs/fuse/dev.c

@@ -1849,7 +1849,7 @@ static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
 	unsigned int num;
 	unsigned int offset;
 	size_t total_len = 0;
-	unsigned int num_pages, cur_pages = 0;
+	unsigned int num_pages;
 	struct fuse_conn *fc = fm->fc;
 	struct fuse_retrieve_args *ra;
 	size_t args_size = sizeof(*ra);
@@ -1867,6 +1867,7 @@ static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
 
 	num_pages = (num + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	num_pages = min(num_pages, fc->max_pages);
+	num = min(num, num_pages << PAGE_SHIFT);
 
 	args_size += num_pages * (sizeof(ap->folios[0]) + sizeof(ap->descs[0]));
 
@@ -1887,25 +1888,29 @@ static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
 
 	index = outarg->offset >> PAGE_SHIFT;
 
-	while (num && cur_pages < num_pages) {
+	while (num) {
 		struct folio *folio;
-		unsigned int this_num;
+		unsigned int folio_offset;
+		unsigned int nr_bytes;
+		unsigned int nr_pages;
 
 		folio = filemap_get_folio(mapping, index);
 		if (IS_ERR(folio))
 			break;
 
-		this_num = min_t(unsigned, num, PAGE_SIZE - offset);
+		folio_offset = ((index - folio->index) << PAGE_SHIFT) + offset;
+		nr_bytes = min(folio_size(folio) - folio_offset, num);
+		nr_pages = (offset + nr_bytes + PAGE_SIZE - 1) >> PAGE_SHIFT;
+
 		ap->folios[ap->num_folios] = folio;
-		ap->descs[ap->num_folios].offset = offset;
-		ap->descs[ap->num_folios].length = this_num;
+		ap->descs[ap->num_folios].offset = folio_offset;
+		ap->descs[ap->num_folios].length = nr_bytes;
 		ap->num_folios++;
-		cur_pages++;
 
 		offset = 0;
-		num -= this_num;
-		total_len += this_num;
-		index++;
+		num -= nr_bytes;
+		total_len += nr_bytes;
+		index += nr_pages;
 	}
 	ra->inarg.offset = outarg->offset;
 	ra->inarg.size = total_len;