squashfs: make squashfs_cache_init() return ERR_PTR(-ENOMEM)

Patch series "squashfs: reduce memory usage and update docs".

This patchset reduces the amount of memory that Squashfs uses when
CONFIG_FILE_DIRECT is configured, and updates various out of date
information in the documentation and Kconfig.

This patch (of 4):

Make squashfs_cache_init() return an ERR_PTR(-ENOMEM) on failure rather
than NULL.

This tidies up some calling code, but, it also allows NULL to be returned
as a valid result when a cache hasn't be allocated.

Link: https://lkml.kernel.org/r/20241229233752.54481-1-phillip@squashfs.org.uk
Link: https://lkml.kernel.org/r/20241229233752.54481-2-phillip@squashfs.org.uk
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/squashfs/cache.c

@@ -224,11 +224,15 @@ struct squashfs_cache *squashfs_cache_init(char *name, int entries,
 	int block_size)
 {
 	int i, j;
-	struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
+	struct squashfs_cache *cache;
 
+	if (entries == 0)
+		return NULL;
+
+	cache = kzalloc(sizeof(*cache), GFP_KERNEL);
 	if (cache == NULL) {
 		ERROR("Failed to allocate %s cache\n", name);
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 	}
 
 	cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
@@ -281,7 +285,7 @@ struct squashfs_cache *squashfs_cache_init(char *name, int entries,
 
 cleanup:
 	squashfs_cache_delete(cache);
-	return NULL;
+	return ERR_PTR(-ENOMEM);
 }
 
 

fs/squashfs/super.c

@@ -314,26 +314,29 @@ static int squashfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_flags |= SB_RDONLY;
 	sb->s_op = &squashfs_super_ops;
 
-	err = -ENOMEM;
-
 	msblk->block_cache = squashfs_cache_init("metadata",
 			SQUASHFS_CACHED_BLKS, SQUASHFS_METADATA_SIZE);
-	if (msblk->block_cache == NULL)
+	if (IS_ERR(msblk->block_cache)) {
+		err = PTR_ERR(msblk->block_cache);
 		goto failed_mount;
+	}
 
 	/* Allocate read_page block */
 	msblk->read_page = squashfs_cache_init("data",
 		msblk->max_thread_num, msblk->block_size);
-	if (msblk->read_page == NULL) {
+	if (IS_ERR(msblk->read_page)) {
 		errorf(fc, "Failed to allocate read_page block");
+		err = PTR_ERR(msblk->read_page);
 		goto failed_mount;
 	}
 
 	if (msblk->devblksize == PAGE_SIZE) {
 		struct inode *cache = new_inode(sb);
 
-		if (cache == NULL)
+		if (cache == NULL) {
+			err = -ENOMEM;
 			goto failed_mount;
+		}
 
 		set_nlink(cache, 1);
 		cache->i_size = OFFSET_MAX;
@@ -406,8 +409,8 @@ static int squashfs_fill_super(struct super_block *sb, struct fs_context *fc)
 
 	msblk->fragment_cache = squashfs_cache_init("fragment",
 		min(SQUASHFS_CACHED_FRAGMENTS, fragments), msblk->block_size);
-	if (msblk->fragment_cache == NULL) {
-		err = -ENOMEM;
+	if (IS_ERR(msblk->fragment_cache)) {
+		err = PTR_ERR(msblk->fragment_cache);
 		goto failed_mount;
 	}