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SubjectRe: RFC: direct MTD support for SquashFS
Date
Peter Korsgaard <jacmet@sunsite.dk> writes:

>>>>>> "Ferenc" == Ferenc Wagner <wferi@niif.hu> writes:
>
> Ferenc> In embedded systems, SquashFS over MTD would be a considerable
> Ferenc> win, as that would permit configuring without CONFIG_BLOCK.
> Ferenc> Please find attached a naive patch against 2.6.33 for this. It
> Ferenc> does not handle bad MTD blocks, that could be handled by gluebi
> Ferenc> (once you're willing to take the UBI overhead), or by a custom
> Ferenc> solution later.
>
> Ferenc> For now, 2.6.34 gained pluggable decompressors, so this patch
> Ferenc> does not apply anymore, though the main idea holds. My
> Ferenc> questions: is the community interested in integrating something
> Ferenc> like this, should this patch transformed into something
> Ferenc> acceptable, or am I a total lunatic? I don't know a thing
> Ferenc> about filesystem development, but willing to learn and
> Ferenc> refactor. Comments welcome.
>
> Nice, I have been thinking about that as well. What kind of size savings
> are you getting with this?

I could only compare apples to oranges before porting the patch to the
LZMA variant. So I refrain from that for a couple of days yet. But
meanwhile I started adding a pluggable backend framework to SquashFS,
and would much appreciate some comments about the applicability of this
idea. The patch is (intended to be) a no-op, applies on top of current
git (a3d3203e4bb40f253b1541e310dc0f9305be7c84).
--
Thanks,
Feri.

From bbed39c4402d563598dc8034514fd66648f835f5 Mon Sep 17 00:00:00 2001
From: Ferenc Wagner <wferi@niif.hu>
Date: Thu, 18 Mar 2010 03:12:01 +0100
Subject: [PATCH] squashfs: add backend plugin framework

---
fs/squashfs/Kconfig | 2 +-
fs/squashfs/Makefile | 4 +-
fs/squashfs/backend.c | 27 ++++++++++
fs/squashfs/backend.h | 22 +++++++++
fs/squashfs/bdev.c | 108 ++++++++++++++++++++++++++++++++++++++++++
fs/squashfs/mtd.c | 82 ++++++++++++++++++++++++++++++++
fs/squashfs/squashfs.h | 12 ++++-
fs/squashfs/squashfs_fs_sb.h | 2 +
8 files changed, 256 insertions(+), 3 deletions(-)
create mode 100644 fs/squashfs/backend.c
create mode 100644 fs/squashfs/backend.h
create mode 100644 fs/squashfs/bdev.c
create mode 100644 fs/squashfs/mtd.c
diff --git a/fs/squashfs/Kconfig b/fs/squashfs/Kconfig
index 25a00d1..5a0de30 100644
--- a/fs/squashfs/Kconfig
+++ b/fs/squashfs/Kconfig
@@ -1,6 +1,6 @@
config SQUASHFS
tristate "SquashFS 4.0 - Squashed file system support"
- depends on BLOCK
+ depends on BLOCK || MTD
select ZLIB_INFLATE
help
Saying Y here includes support for SquashFS 4.0 (a Compressed
diff --git a/fs/squashfs/Makefile b/fs/squashfs/Makefile
index df8a19e..49230e3 100644
--- a/fs/squashfs/Makefile
+++ b/fs/squashfs/Makefile
@@ -4,4 +4,6 @@

obj-$(CONFIG_SQUASHFS) += squashfs.o
squashfs-y += block.o cache.o dir.o export.o file.o fragment.o id.o inode.o
-squashfs-y += namei.o super.o symlink.o zlib_wrapper.o decompressor.o
+squashfs-y += namei.o super.o symlink.o zlib_wrapper.o decompressor.o backend.o
+squashfs-$(CONFIG_BLOCK) += bdev.o
+squashfs-$(CONFIG_MTD) += mtd.o
diff --git a/fs/squashfs/backend.c b/fs/squashfs/backend.c
new file mode 100644
index 0000000..1b197c8
--- /dev/null
+++ b/fs/squashfs/backend.c
@@ -0,0 +1,27 @@
+#include <linux/fs.h>
+
+#include "squashfs_fs_i.h"
+#include "squashfs.h"
+#include "backend.h"
+
+const struct squashfs_backend *backends[] = {
+#ifdef CONFIG_BLOCK
+ &squashfs_bdev_ops,
+#endif
+#ifdef CONFIG_MTD
+ &squashfs_mtd_ops,
+#endif
+ NULL
+};
+
+const struct squashfs_backend *
+squashfs_find_backend(struct file_system_type *fs_type, int flags,
+ const char *dev_name, void *data, struct vfsmount *mnt)
+{
+ const struct squashfs_backend **b;
+
+ for (b = backends; *b; b++)
+ if (!(*b)->probe(fs_type, flags, dev_name, data, mnt))
+ break;
+ return *b;
+}
diff --git a/fs/squashfs/backend.h b/fs/squashfs/backend.h
new file mode 100644
index 0000000..58c3476
--- /dev/null
+++ b/fs/squashfs/backend.h
@@ -0,0 +1,22 @@
+#include <linux/fs.h>
+#include <linux/vfs.h>
+
+#include "squashfs_fs_sb.h"
+
+struct squashfs_backend {
+ void *(*init)(struct squashfs_sb_info *, u64, size_t);
+ void (*free)(struct squashfs_sb_info *);
+ ssize_t (*read)(struct squashfs_sb_info *, void **, size_t);
+ int (*probe)(struct file_system_type *, int, const char *,
+ void*, struct vfsmount *);
+ void (*kill)(struct squashfs_sb_info *);
+ loff_t (*size)(const struct super_block *);
+ const char *(*devname)(const struct super_block *, char *);
+};
+
+/* Dummy, until the original is nuked */
+static inline int squashfs_fill_super2(struct super_block *sb, void *data,
+ int silent, const struct squashfs_backend *ops)
+{
+ return -1;
+}
diff --git a/fs/squashfs/bdev.c b/fs/squashfs/bdev.c
new file mode 100644
index 0000000..8ba2322
--- /dev/null
+++ b/fs/squashfs/bdev.c
@@ -0,0 +1,108 @@
+#include <linux/fs.h>
+#include <linux/buffer_head.h>
+
+#include "squashfs_fs_i.h"
+#include "squashfs.h"
+#include "backend.h"
+
+struct squashfs_bdev {
+ int devblksize; /* FIXME: == s->s_blocksize(_bits)? */
+ unsigned short devblksize_log2;
+ size_t bytes_left;
+ struct buffer_head **bh;
+ int bh_index; /* number of consumed buffer_heads */
+ int offset; /* offset of next byte in buffer_head */
+};
+
+/* A backend is initialized for each SquashFS block read operation,
+ * making further sequential reads possible from the block.
+ */
+static void *bdev_init(struct squashfs_sb_info *msblk, u64 index, size_t length)
+{
+ struct squashfs_bdev *bdev = msblk->backend_data;
+ struct buffer_head *bh;
+
+ bh = kcalloc((msblk->block_size >> bdev->devblksize_log2) + 1,
+ sizeof(*bh), GFP_KERNEL);
+ if (!bh)
+ goto nomem;
+
+ /* different preread for data blocks and metadata blocks */
+
+ bdev->bh_index = 0;
+ bdev->bytes_left = length;
+ return bdev;
+
+nomem:
+ ERROR("failed to allocate buffer_heads\n");
+ return NULL;
+}
+
+static void bdev_free(struct squashfs_sb_info *msblk)
+{
+ struct squashfs_bdev *bdev = msblk->backend_data;
+ kfree(bdev->bh);
+ bdev->bh = 0; /* FIXME: to make bdev_kill universal (see there) */
+}
+
+static ssize_t bdev_read(struct squashfs_sb_info *msblk, void **buf, size_t len)
+{
+ return -ENOSYS;
+}
+
+static int fill_bdev_super(struct super_block *sb, void *data, int silent)
+{
+ struct squashfs_sb_info *msblk;
+ struct squashfs_bdev *bdev;
+ int err = squashfs_fill_super2(sb, data, silent, &squashfs_bdev_ops);
+ if (err)
+ return err;
+
+ bdev = kzalloc(sizeof(*bdev), GFP_KERNEL);
+ if (!bdev)
+ return -ENOMEM;
+
+ bdev->devblksize = sb_min_blocksize(sb, BLOCK_SIZE);
+ bdev->devblksize_log2 = ffz(~bdev->devblksize);
+
+ msblk = sb->s_fs_info;
+ msblk->backend_data = bdev;
+ return 0;
+}
+
+static int bdev_probe(struct file_system_type *fs_type, int flags,
+ const char *dev_name, void *data,
+ struct vfsmount *mnt)
+{
+ return get_sb_bdev(fs_type, flags, dev_name, data,
+ fill_bdev_super, mnt);
+}
+
+static void bdev_kill(struct squashfs_sb_info *msblk)
+{
+ struct squashfs_bdev *bdev = msblk->backend_data;
+ if (bdev) {
+ kfree(bdev->bh); /* FIXME: can this be nonzero? cf. bdev_free */
+ kfree(bdev);
+ }
+}
+
+static loff_t bdev_size(const struct super_block *sb)
+{
+ return i_size_read(sb->s_bdev->bd_inode);
+}
+
+static const char *bdev_devname(const struct super_block *sb, char *buffer)
+{
+ return bdevname(sb->s_bdev, buffer);
+}
+
+const struct squashfs_backend squashfs_bdev_ops = {
+ .init = bdev_init,
+ .free = bdev_free,
+ .read = bdev_read,
+ .probe = bdev_probe,
+ .kill = bdev_kill,
+ .size = bdev_size,
+ .devname= bdev_devname
+};
diff --git a/fs/squashfs/mtd.c b/fs/squashfs/mtd.c
new file mode 100644
index 0000000..c63b4f8
--- /dev/null
+++ b/fs/squashfs/mtd.c
@@ -0,0 +1,82 @@
+#include <linux/fs.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/super.h>
+
+#include "squashfs_fs_i.h"
+#include "squashfs.h"
+#include "backend.h"
+
+struct squashfs_mtd {
+ size_t bytes_left;
+};
+
+/* A backend is initialized for each SquashFS block read operation,
+ * making further sequential reads possible from the block.
+ */
+static void *mtd_init(struct squashfs_sb_info *msblk, u64 index, size_t length)
+{
+ struct squashfs_mtd *mtd = msblk->backend_data;
+
+ mtd->bytes_left = length;
+ return mtd;
+}
+
+static void mtd_free(struct squashfs_sb_info *msblk)
+{
+}
+
+static ssize_t mtd_read(struct squashfs_sb_info *msblk, void **buf, size_t len)
+{
+ return -ENOSYS;
+}
+
+static int fill_mtd_super(struct super_block *sb, void *data, int silent)
+{
+ struct squashfs_sb_info *msblk;
+ struct squashfs_mtd *mtd;
+ int err = squashfs_fill_super2(sb, data, silent, &squashfs_mtd_ops);
+ if (err)
+ return err;
+
+ mtd = kzalloc(sizeof(*mtd), GFP_KERNEL);
+ if (!mtd)
+ return -ENOMEM;
+
+ msblk = sb->s_fs_info;
+ msblk->backend_data = mtd;
+ return 0;
+}
+
+static int mtd_probe(struct file_system_type *fs_type, int flags,
+ const char *dev_name, void *data,
+ struct vfsmount *mnt)
+{
+ return get_sb_mtd(fs_type, flags, dev_name, data,
+ fill_mtd_super, mnt);
+}
+
+static void mtd_kill(struct squashfs_sb_info *msblk)
+{
+ kfree(msblk->backend_data);
+}
+
+static loff_t mtd_size(const struct super_block *sb)
+{
+ return sb->s_mtd->size;
+}
+
+static const char *mtd_devname(const struct super_block *sb, char *buffer)
+{
+ snprintf(buffer, BDEVNAME_SIZE, "MTD%d", sb->s_mtd->index);
+ return buffer;
+}
+
+const struct squashfs_backend squashfs_mtd_ops = {
+ .init = mtd_init,
+ .free = mtd_free,
+ .read = mtd_read,
+ .probe = mtd_probe,
+ .kill = mtd_kill,
+ .size = mtd_size,
+ .devname= mtd_devname
+};
diff --git a/fs/squashfs/squashfs.h b/fs/squashfs/squashfs.h
index fe2587a..3efa18f 100644
--- a/fs/squashfs/squashfs.h
+++ b/fs/squashfs/squashfs.h
@@ -73,8 +73,12 @@ extern struct inode *squashfs_iget(struct super_block *, long long,
unsigned int);
extern int squashfs_read_inode(struct inode *, long long);

+/* super.c
+int squashfs_fill_super(struct super_block *, void *, int,
+ struct squashfs_backend *);
+*/
/*
- * Inodes, files and decompressor operations
+ * Inodes, files, backend and decompressor operations
*/

/* dir.c */
@@ -94,3 +98,9 @@ extern const struct address_space_operations squashfs_symlink_aops;

/* zlib_wrapper.c */
extern const struct squashfs_decompressor squashfs_zlib_comp_ops;
+
+/* bdev.c */
+extern const struct squashfs_backend squashfs_bdev_ops;
+
+/* mtd.c */
+extern const struct squashfs_backend squashfs_mtd_ops;
diff --git a/fs/squashfs/squashfs_fs_sb.h b/fs/squashfs/squashfs_fs_sb.h
index 2e77dc5..378b0ad 100644
--- a/fs/squashfs/squashfs_fs_sb.h
+++ b/fs/squashfs/squashfs_fs_sb.h
@@ -53,6 +53,8 @@ struct squashfs_cache_entry {

struct squashfs_sb_info {
const struct squashfs_decompressor *decompressor;
+ const struct squashfs_backend *backend;
+ void *backend_data;
int devblksize;
int devblksize_log2;
struct squashfs_cache *block_cache;
--
1.5.6.5
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