Squashfs: Refactor decompressor interface and code

The decompressor interface and code was written from
the point of view of single-threaded operation.  In doing
so it mixed a lot of single-threaded implementation specific
aspects into the decompressor code and elsewhere which makes it
difficult to seamlessly support multiple different decompressor
implementations.

This patch does the following:

1.  It removes compressor_options parsing from the decompressor
    init() function.  This allows the decompressor init() function
    to be dynamically called to instantiate multiple decompressors,
    without the compressor options needing to be read and parsed each
    time.

2.  It moves threading and all sleeping operations out of the
    decompressors.  In doing so, it makes the decompressors
    non-blocking wrappers which only deal with interfacing with
    the decompressor implementation.

3. It splits decompressor.[ch] into decompressor generic functions
   in decompressor.[ch], and moves the single threaded
   decompressor implementation into decompressor_single.c.

The result of this patch is Squashfs should now be able to
support multiple decompressors by adding new decompressor_xxx.c
files with specialised implementations of the functions in
decompressor_single.c

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reviewed-by: Minchan Kim <minchan@kernel.org>

1 files changed, 32 insertions, 15 deletions

diff --git a/fs/squashfs/decompressor.c b/fs/squashfs/decompressor.c
index 3f6271d86abc..234291f79ba5 100644
--- a/fs/squashfs/decompressor.c
+++ b/fs/squashfs/decompressor.c
@@ -37,29 +37,29 @@
  */
 
 static const struct squashfs_decompressor squashfs_lzma_unsupported_comp_ops = {
-	NULL, NULL, NULL, LZMA_COMPRESSION, "lzma", 0
+	NULL, NULL, NULL, NULL, LZMA_COMPRESSION, "lzma", 0
 };
 
 #ifndef CONFIG_SQUASHFS_LZO
 static const struct squashfs_decompressor squashfs_lzo_comp_ops = {
-	NULL, NULL, NULL, LZO_COMPRESSION, "lzo", 0
+	NULL, NULL, NULL, NULL, LZO_COMPRESSION, "lzo", 0
 };
 #endif
 
 #ifndef CONFIG_SQUASHFS_XZ
 static const struct squashfs_decompressor squashfs_xz_comp_ops = {
-	NULL, NULL, NULL, XZ_COMPRESSION, "xz", 0
+	NULL, NULL, NULL, NULL, XZ_COMPRESSION, "xz", 0
 };
 #endif
 
 #ifndef CONFIG_SQUASHFS_ZLIB
 static const struct squashfs_decompressor squashfs_zlib_comp_ops = {
-	NULL, NULL, NULL, ZLIB_COMPRESSION, "zlib", 0
+	NULL, NULL, NULL, NULL, ZLIB_COMPRESSION, "zlib", 0
 };
 #endif
 
 static const struct squashfs_decompressor squashfs_unknown_comp_ops = {
-	NULL, NULL, NULL, 0, "unknown", 0
+	NULL, NULL, NULL, NULL, 0, "unknown", 0
 };
 
 static const struct squashfs_decompressor *decompressor[] = {
@@ -83,10 +83,10 @@ const struct squashfs_decompressor *squashfs_lookup_decompressor(int id)
 }
 
 
-void *squashfs_decompressor_init(struct super_block *sb, unsigned short flags)
+static void *get_comp_opts(struct super_block *sb, unsigned short flags)
 {
 	struct squashfs_sb_info *msblk = sb->s_fs_info;
-	void *strm, *buffer = NULL;
+	void *buffer = NULL, *comp_opts;
 	int length = 0;
 
 	/*
@@ -94,23 +94,40 @@ void *squashfs_decompressor_init(struct super_block *sb, unsigned short flags)
 	 */
 	if (SQUASHFS_COMP_OPTS(flags)) {
 		buffer = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
-		if (buffer == NULL)
-			return ERR_PTR(-ENOMEM);
+		if (buffer == NULL) {
+			comp_opts = ERR_PTR(-ENOMEM);
+			goto out;
+		}
 
 		length = squashfs_read_data(sb, &buffer,
 			sizeof(struct squashfs_super_block), 0, NULL,
-			PAGE_CACHE_SIZE, 1);
+				PAGE_CACHE_SIZE, 1);
 
 		if (length < 0) {
-			strm = ERR_PTR(length);
-			goto finished;
+			comp_opts = ERR_PTR(length);
+			goto out;
 		}
 	}
 
-	strm = msblk->decompressor->init(msblk, buffer, length);
+	comp_opts = squashfs_comp_opts(msblk, buffer, length);
 
-finished:
+out:
 	kfree(buffer);
+	return comp_opts;
+}
+
+
+void *squashfs_decompressor_setup(struct super_block *sb, unsigned short flags)
+{
+	struct squashfs_sb_info *msblk = sb->s_fs_info;
+	void *stream, *comp_opts = get_comp_opts(sb, flags);
+
+	if (IS_ERR(comp_opts))
+		return comp_opts;
+
+	stream = squashfs_decompressor_create(msblk, comp_opts);
+	if (IS_ERR(stream))
+		kfree(comp_opts);
 
-	return strm;
+	return stream;
 }