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[PATCH v2 0/5] cramfs refresh for embedded usage

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  [PATCH v2 0/5] cramfs refresh for embedded usage Nicolas Pitre <nicolas.pitre@linaro.org> - 2017-08-16 19:40 +0200
    [PATCH v2 2/5] cramfs: make cramfs_physmem usable as root fs Nicolas Pitre <nicolas.pitre@linaro.org> - 2017-08-16 19:40 +0200
    [PATCH v2 1/5] cramfs: direct memory access support Nicolas Pitre <nicolas.pitre@linaro.org> - 2017-08-16 19:40 +0200
      RE: [PATCH v2 1/5] cramfs: direct memory access support Chris Brandt <Chris.Brandt@renesas.com> - 2017-08-16 20:30 +0200
        RE: [PATCH v2 1/5] cramfs: direct memory access support Nicolas Pitre <nicolas.pitre@linaro.org> - 2017-08-16 21:50 +0200
    [PATCH v2 3/5] cramfs: implement uncompressed and arbitrary data block positioning Nicolas Pitre <nicolas.pitre@linaro.org> - 2017-08-16 19:40 +0200
      RE: [PATCH v2 3/5] cramfs: implement uncompressed and arbitrary data  block positioning Chris Brandt <Chris.Brandt@renesas.com> - 2017-08-16 20:30 +0200

#1713183 — [PATCH v2 0/5] cramfs refresh for embedded usage

This series brings a nice refresh to the cramfs filesystem, adding the
following capabilities:

- Direct memory access, bypassing the block and/or MTD layers entirely.

- Ability to store individual data blocks uncompressed.

- Ability to locate individual data blocks anywhere in the filesystem.

The end result is a very tight filesystem that can be accessed directly
from ROM without any other subsystem underneath. Also this allows for
user space XIP which is a very important feature for tiny embedded
systems.

Why cramfs?

  Because cramfs is very simple and small. With CONFIG_CRAMFS_BLOCK=n and
  CONFIG_CRAMFS_PHYSMEM=y the cramfs driver may use as little as 3704 bytes
  of code. That's many times smaller than squashfs. And the runtime memory
  usage is also much less with cramfs than squashfs. It packs very tightly
  already compared to romfs which has no compression support. And the cramfs
  format was simple to extend, allowing for both compressed and uncompressed
  blocks within the same file.

Why not accessing ROM via MTD?

  The MTD layer is nice and flexible. It also represents a huge overhead
  considering its core with no other enabled options weights 19KB.
  That's many times the size of the cramfs code for something that
  essentially boils down to a glorified argument parser and a call to
  memremap() in this case.  And if someone still wants to use cramfs via
  MTD then it is already possible with mtdblock.

Why not using DAX?

  DAX stands for "Direct Access" and is a generic kernel layer helping
  with the necessary tasks involved with XIP. It is tailored for large
  writable filesystems and relies on the presence of an MMU. It also has
  the following shortcoming: "The DAX code does not work correctly on
  architectures which have virtually mapped caches such as ARM, MIPS and
  SPARC." That makes it unsuitable for a large portion of the intended
  targets for this series. And due to the read-only nature of cramfs, it is
  possible to achieve the intended result with a much simpler approach making
  DAX somewhat overkill in this context.

The maximum size of a cramfs image can't exceed 272MB. In practice it is
likely to be much much less. Given this series is concerned with small
memory systems, even in the MMU case there is always plenty of vmalloc
space left to map it all and even a 272MB memremap() wouldn't be a
problem. If it is then maybe your system is big enough with large
resources to manage already and you're pretty unlikely to be using cramfs
in the first place.

Of course, while this cramfs remains backward compatible with existing
filesystem images, a newer mkcramfs version is necessary to take advantage
of the extended data layout. I created a version of mkcramfs that
detects ELF files and marks text+rodata segments for XIP and compresses the
rest of those ELF files automatically.

So here it is. I'm also willing to step up as cramfs maintainer given
that no sign of any maintenance activities appeared for years.

This series is also available based on v4.13-rc4 via git here:

  http://git.linaro.org/people/nicolas.pitre/linux xipcramfs


Changes from v1:

- Improved mmap() support by adding the ability to partially populate a
  mapping and lazily split the non directly mapable pages to a separate
  vma at fault time (thanks to Chris Brandt for testing).

- Clarified the documentation some more.


diffstat:

 Documentation/filesystems/cramfs.txt |  42 ++
 MAINTAINERS                          |   4 +-
 fs/cramfs/Kconfig                    |  39 +-
 fs/cramfs/README                     |  31 +-
 fs/cramfs/inode.c                    | 621 +++++++++++++++++++++++++----
 include/uapi/linux/cramfs_fs.h       |  20 +-
 init/do_mounts.c                     |   8 +
 7 files changed, 688 insertions(+), 77 deletions(-)

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#1713184 — [PATCH v2 2/5] cramfs: make cramfs_physmem usable as root fs

Signed-off-by: Nicolas Pitre <nico@linaro.org>
---
 init/do_mounts.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/init/do_mounts.c b/init/do_mounts.c
index c2de5104aa..43b5817f60 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -556,6 +556,14 @@ void __init prepare_namespace(void)
 		ssleep(root_delay);
 	}
 
+	if (IS_ENABLED(CONFIG_CRAMFS_PHYSMEM) && root_fs_names &&
+	    !strcmp(root_fs_names, "cramfs_physmem")) {
+		int err = do_mount_root("cramfs", "cramfs_physmem",
+					root_mountflags, root_mount_data);
+		if (!err)
+			goto out;
+	}
+
 	/*
 	 * wait for the known devices to complete their probing
 	 *
-- 
2.9.5

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#1713185 — [PATCH v2 1/5] cramfs: direct memory access support

Small embedded systems typically execute the kernel code in place (XIP)
directly from flash to save on precious RAM usage. This adds the ability
to consume filesystem data directly from flash to the cramfs filesystem
as well. Cramfs is particularly well suited to this feature as it is
very simple and its RAM usage is already very low, and with this feature
it is possible to use it with no block device support and even lower RAM
usage.

This patch was inspired by a similar patch from Shane Nay dated 17 years
ago that used to be very popular in embedded circles but never made it
into mainline. This is a cleaned-up implementation that uses far fewer
memory address at run time when both methods are configured in. In the
context of small IoT deployments, this functionality has become relevant and useful again.

To distinguish between both access types, the cramfs_physmem filesystem
type must be specified when using a memory accessible cramfs image, and
the physaddr argument must provide the actual filesystem image's physical
memory location.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
---
 fs/cramfs/Kconfig |  30 ++++++-
 fs/cramfs/inode.c | 264 +++++++++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 242 insertions(+), 52 deletions(-)

diff --git a/fs/cramfs/Kconfig b/fs/cramfs/Kconfig
index 11b29d491b..5eed4ad2d5 100644
--- a/fs/cramfs/Kconfig
+++ b/fs/cramfs/Kconfig
@@ -1,6 +1,5 @@
 config CRAMFS
 	tristate "Compressed ROM file system support (cramfs) (OBSOLETE)"
-	depends on BLOCK
 	select ZLIB_INFLATE
 	help
 	  Saying Y here includes support for CramFs (Compressed ROM File
@@ -20,3 +19,32 @@ config CRAMFS
 	  in terms of performance and features.
 
 	  If unsure, say N.
+
+config CRAMFS_BLOCKDEV
+	bool "Support CramFs image over a regular block device" if EXPERT
+	depends on CRAMFS && BLOCK
+	default y
+	help
+	  This option allows the CramFs driver to load data from a regular
+	  block device such a disk partition or a ramdisk.
+	  
+config CRAMFS_PHYSMEM
+	bool "Support CramFs image directly mapped in physical memory"
+	depends on CRAMFS
+	default y if !CRAMFS_BLOCKDEV
+	help
+	  This option allows the CramFs driver to load data directly from
+	  a linear adressed memory range (usually non volatile memory
+	  like flash) instead of going through the block device layer.
+	  This saves some memory since no intermediate buffering is
+	  necessary.
+
+	  The filesystem type for this feature is "cramfs_physmem".
+	  The location of the CramFs image in memory is board
+	  dependent. Therefore, if you say Y, you must know the proper
+	  physical address where to store the CramFs image and specify
+	  it using the physaddr=0x******** mount option (for example:
+	  "mount -t cramfs_physmem -o physaddr=0x100000 none /mnt").
+
+	  If unsure, say N.
+
diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index 7919967488..393eb27ef4 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -24,6 +24,7 @@
 #include <linux/mutex.h>
 #include <uapi/linux/cramfs_fs.h>
 #include <linux/uaccess.h>
+#include <linux/io.h>
 
 #include "internal.h"
 
@@ -36,6 +37,8 @@ struct cramfs_sb_info {
 	unsigned long blocks;
 	unsigned long files;
 	unsigned long flags;
+	void *linear_virt_addr;
+	phys_addr_t linear_phys_addr;
 };
 
 static inline struct cramfs_sb_info *CRAMFS_SB(struct super_block *sb)
@@ -140,6 +143,9 @@ static struct inode *get_cramfs_inode(struct super_block *sb,
  * BLKS_PER_BUF*PAGE_SIZE, so that the caller doesn't need to
  * worry about end-of-buffer issues even when decompressing a full
  * page cache.
+ *
+ * Note: This is all optimized away at compile time when
+ *       CONFIG_CRAMFS_BLOCKDEV=n.
  */
 #define READ_BUFFERS (2)
 /* NEXT_BUFFER(): Loop over [0..(READ_BUFFERS-1)]. */
@@ -160,10 +166,10 @@ static struct super_block *buffer_dev[READ_BUFFERS];
 static int next_buffer;
 
 /*
- * Returns a pointer to a buffer containing at least LEN bytes of
- * filesystem starting at byte offset OFFSET into the filesystem.
+ * Populate our block cache and return a pointer from it.
  */
-static void *cramfs_read(struct super_block *sb, unsigned int offset, unsigned int len)
+static void *cramfs_blkdev_read(struct super_block *sb, unsigned int offset,
+				unsigned int len)
 {
 	struct address_space *mapping = sb->s_bdev->bd_inode->i_mapping;
 	struct page *pages[BLKS_PER_BUF];
@@ -239,7 +245,39 @@ static void *cramfs_read(struct super_block *sb, unsigned int offset, unsigned i
 	return read_buffers[buffer] + offset;
 }
 
-static void cramfs_kill_sb(struct super_block *sb)
+/*
+ * Return a pointer to the linearly addressed cramfs image in memory.
+ */
+static void *cramfs_direct_read(struct super_block *sb, unsigned int offset,
+				unsigned int len)
+{
+	struct cramfs_sb_info *sbi = CRAMFS_SB(sb);
+
+	if (!len)
+		return NULL;
+	if (len > sbi->size || offset > sbi->size - len)
+	       return page_address(ZERO_PAGE(0));	
+	return sbi->linear_virt_addr + offset;
+}
+
+/*
+ * Returns a pointer to a buffer containing at least LEN bytes of
+ * filesystem starting at byte offset OFFSET into the filesystem.
+ */
+static void *cramfs_read(struct super_block *sb, unsigned int offset,
+			 unsigned int len)
+{
+	struct cramfs_sb_info *sbi = CRAMFS_SB(sb);
+
+	if (IS_ENABLED(CONFIG_CRAMFS_PHYSMEM) && sbi->linear_virt_addr)
+		return cramfs_direct_read(sb, offset, len);
+	else if (IS_ENABLED(CONFIG_CRAMFS_BLOCKDEV))
+		return cramfs_blkdev_read(sb, offset, len);
+	else
+		return NULL;
+}
+
+static void cramfs_blkdev_kill_sb(struct super_block *sb)
 {
 	struct cramfs_sb_info *sbi = CRAMFS_SB(sb);
 
@@ -247,6 +285,16 @@ static void cramfs_kill_sb(struct super_block *sb)
 	kfree(sbi);
 }
 
+static void cramfs_physmem_kill_sb(struct super_block *sb)
+{
+	struct cramfs_sb_info *sbi = CRAMFS_SB(sb);
+
+	if (sbi->linear_virt_addr)
+		memunmap(sbi->linear_virt_addr);
+	kill_anon_super(sb);
+	kfree(sbi);
+}
+
 static int cramfs_remount(struct super_block *sb, int *flags, char *data)
 {
 	sync_filesystem(sb);
@@ -254,34 +302,24 @@ static int cramfs_remount(struct super_block *sb, int *flags, char *data)
 	return 0;
 }
 
-static int cramfs_fill_super(struct super_block *sb, void *data, int silent)
+static int cramfs_read_super(struct super_block *sb,
+			     struct cramfs_super *super, int silent)
 {
-	int i;
-	struct cramfs_super super;
+	struct cramfs_sb_info *sbi = CRAMFS_SB(sb);
 	unsigned long root_offset;
-	struct cramfs_sb_info *sbi;
-	struct inode *root;
-
-	sb->s_flags |= MS_RDONLY;
-
-	sbi = kzalloc(sizeof(struct cramfs_sb_info), GFP_KERNEL);
-	if (!sbi)
-		return -ENOMEM;
-	sb->s_fs_info = sbi;
 
-	/* Invalidate the read buffers on mount: think disk change.. */
-	mutex_lock(&read_mutex);
-	for (i = 0; i < READ_BUFFERS; i++)
-		buffer_blocknr[i] = -1;
+	/* We don't know the real size yet */
+	sbi->size = PAGE_SIZE;
 
 	/* Read the first block and get the superblock from it */
-	memcpy(&super, cramfs_read(sb, 0, sizeof(super)), sizeof(super));
+	mutex_lock(&read_mutex);
+	memcpy(super, cramfs_read(sb, 0, sizeof(*super)), sizeof(*super));
 	mutex_unlock(&read_mutex);
 
 	/* Do sanity checks on the superblock */
-	if (super.magic != CRAMFS_MAGIC) {
+	if (super->magic != CRAMFS_MAGIC) {
 		/* check for wrong endianness */
-		if (super.magic == CRAMFS_MAGIC_WEND) {
+		if (super->magic == CRAMFS_MAGIC_WEND) {
 			if (!silent)
 				pr_err("wrong endianness\n");
 			return -EINVAL;
@@ -289,10 +327,10 @@ static int cramfs_fill_super(struct super_block *sb, void *data, int silent)
 
 		/* check at 512 byte offset */
 		mutex_lock(&read_mutex);
-		memcpy(&super, cramfs_read(sb, 512, sizeof(super)), sizeof(super));
+		memcpy(super, cramfs_read(sb, 512, sizeof(*super)), sizeof(*super));
 		mutex_unlock(&read_mutex);
-		if (super.magic != CRAMFS_MAGIC) {
-			if (super.magic == CRAMFS_MAGIC_WEND && !silent)
+		if (super->magic != CRAMFS_MAGIC) {
+			if (super->magic == CRAMFS_MAGIC_WEND && !silent)
 				pr_err("wrong endianness\n");
 			else if (!silent)
 				pr_err("wrong magic\n");
@@ -301,34 +339,34 @@ static int cramfs_fill_super(struct super_block *sb, void *data, int silent)
 	}
 
 	/* get feature flags first */
-	if (super.flags & ~CRAMFS_SUPPORTED_FLAGS) {
+	if (super->flags & ~CRAMFS_SUPPORTED_FLAGS) {
 		pr_err("unsupported filesystem features\n");
 		return -EINVAL;
 	}
 
 	/* Check that the root inode is in a sane state */
-	if (!S_ISDIR(super.root.mode)) {
+	if (!S_ISDIR(super->root.mode)) {
 		pr_err("root is not a directory\n");
 		return -EINVAL;
 	}
 	/* correct strange, hard-coded permissions of mkcramfs */
-	super.root.mode |= (S_IRUSR | S_IXUSR | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
+	super->root.mode |= (S_IRUSR | S_IXUSR | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
 
-	root_offset = super.root.offset << 2;
-	if (super.flags & CRAMFS_FLAG_FSID_VERSION_2) {
-		sbi->size = super.size;
-		sbi->blocks = super.fsid.blocks;
-		sbi->files = super.fsid.files;
+	root_offset = super->root.offset << 2;
+	if (super->flags & CRAMFS_FLAG_FSID_VERSION_2) {
+		sbi->size = super->size;
+		sbi->blocks = super->fsid.blocks;
+		sbi->files = super->fsid.files;
 	} else {
 		sbi->size = 1<<28;
 		sbi->blocks = 0;
 		sbi->files = 0;
 	}
-	sbi->magic = super.magic;
-	sbi->flags = super.flags;
+	sbi->magic = super->magic;
+	sbi->flags = super->flags;
 	if (root_offset == 0)
 		pr_info("empty filesystem");
-	else if (!(super.flags & CRAMFS_FLAG_SHIFTED_ROOT_OFFSET) &&
+	else if (!(super->flags & CRAMFS_FLAG_SHIFTED_ROOT_OFFSET) &&
 		 ((root_offset != sizeof(struct cramfs_super)) &&
 		  (root_offset != 512 + sizeof(struct cramfs_super))))
 	{
@@ -336,9 +374,18 @@ static int cramfs_fill_super(struct super_block *sb, void *data, int silent)
 		return -EINVAL;
 	}
 
+	return 0;
+}
+
+static int cramfs_finalize_super(struct super_block *sb,
+				 struct cramfs_inode *cramfs_root)
+{
+	struct inode *root;
+
 	/* Set it all up.. */
+	sb->s_flags |= MS_RDONLY;
 	sb->s_op = &cramfs_ops;
-	root = get_cramfs_inode(sb, &super.root, 0);
+	root = get_cramfs_inode(sb, cramfs_root, 0);
 	if (IS_ERR(root))
 		return PTR_ERR(root);
 	sb->s_root = d_make_root(root);
@@ -347,6 +394,92 @@ static int cramfs_fill_super(struct super_block *sb, void *data, int silent)
 	return 0;
 }
 
+static int cramfs_blkdev_fill_super(struct super_block *sb, void *data, int silent)
+{
+	struct cramfs_sb_info *sbi;
+	struct cramfs_super super;
+	int i, err;
+
+	sbi = kzalloc(sizeof(struct cramfs_sb_info), GFP_KERNEL);
+	if (!sbi)
+		return -ENOMEM;
+	sb->s_fs_info = sbi;
+
+	/* Invalidate the read buffers on mount: think disk change.. */
+	for (i = 0; i < READ_BUFFERS; i++)
+		buffer_blocknr[i] = -1;
+
+	err = cramfs_read_super(sb, &super, silent);
+	if (err)
+		return err;
+	return cramfs_finalize_super(sb, &super.root);
+}
+
+static int cramfs_physmem_fill_super(struct super_block *sb, void *data, int silent)
+{
+	struct cramfs_sb_info *sbi;
+	struct cramfs_super super;
+	char *p;
+	int err;
+
+	sbi = kzalloc(sizeof(struct cramfs_sb_info), GFP_KERNEL);
+	if (!sbi)
+		return -ENOMEM;
+	sb->s_fs_info = sbi;
+
+	/*
+	 * The physical location of the cramfs image is specified as
+	 * a mount parameter.  This parameter is mandatory for obvious
+	 * reasons.  Some validation is made on the phys address but this
+	 * is not exhaustive and we count on the fact that someone using
+	 * this feature is supposed to know what he/she's doing.
+	 */
+	if (!data || !(p = strstr((char *)data, "physaddr="))) {
+		pr_err("unknown physical address for linear cramfs image\n");
+		return -EINVAL;
+	}
+	sbi->linear_phys_addr = memparse(p + 9, NULL);
+	if (!sbi->linear_phys_addr) {
+		pr_err("bad value for cramfs image physical address\n");
+		return -EINVAL;
+	}
+	if (sbi->linear_phys_addr & (PAGE_SIZE-1)) {
+		pr_err("physical address %pap for linear cramfs isn't aligned to a page boundary\n",
+			&sbi->linear_phys_addr);
+		return -EINVAL;
+	}
+
+	/*
+	 * Map only one page for now.  Will remap it when fs size is known.
+	 * Although we'll only read from it, we want the CPU cache to
+	 * kick in for the higher throughput it provides, hence MEMREMAP_WB.
+	 */
+	pr_info("checking physical address %pap for linear cramfs image\n", &sbi->linear_phys_addr);
+	sbi->linear_virt_addr = memremap(sbi->linear_phys_addr, PAGE_SIZE,
+					 MEMREMAP_WB);
+	if (!sbi->linear_virt_addr) {
+		pr_err("ioremap of the linear cramfs image failed\n");
+		return -ENOMEM;
+	}
+
+	err = cramfs_read_super(sb, &super, silent);
+	if (err)
+		return err;
+
+	/* Remap the whole filesystem now */
+	pr_info("linear cramfs image appears to be %lu KB in size\n",
+		sbi->size/1024);
+	memunmap(sbi->linear_virt_addr);
+	sbi->linear_virt_addr = memremap(sbi->linear_phys_addr, sbi->size,
+					 MEMREMAP_WB);
+	if (!sbi->linear_virt_addr) {
+		pr_err("ioremap of the linear cramfs image failed\n");
+		return -ENOMEM;
+	}
+
+	return cramfs_finalize_super(sb, &super.root);
+}
+
 static int cramfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
 	struct super_block *sb = dentry->d_sb;
@@ -573,38 +706,67 @@ static const struct super_operations cramfs_ops = {
 	.statfs		= cramfs_statfs,
 };
 
-static struct dentry *cramfs_mount(struct file_system_type *fs_type,
-	int flags, const char *dev_name, void *data)
+static struct dentry *cramfs_blkdev_mount(struct file_system_type *fs_type,
+				int flags, const char *dev_name, void *data)
+{
+	return mount_bdev(fs_type, flags, dev_name, data, cramfs_blkdev_fill_super);
+}
+
+static struct dentry *cramfs_physmem_mount(struct file_system_type *fs_type,
+				int flags, const char *dev_name, void *data)
 {
-	return mount_bdev(fs_type, flags, dev_name, data, cramfs_fill_super);
+	return mount_nodev(fs_type, flags, data, cramfs_physmem_fill_super);
 }
 
 static struct file_system_type cramfs_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "cramfs",
-	.mount		= cramfs_mount,
-	.kill_sb	= cramfs_kill_sb,
+	.mount		= cramfs_blkdev_mount,
+	.kill_sb	= cramfs_blkdev_kill_sb,
 	.fs_flags	= FS_REQUIRES_DEV,
 };
+
+static struct file_system_type cramfs_physmem_fs_type = {
+	.owner		= THIS_MODULE,
+	.name		= "cramfs_physmem",
+	.mount		= cramfs_physmem_mount,
+	.kill_sb	= cramfs_physmem_kill_sb,
+};
+
+#ifdef CONFIG_CRAMFS_BLOCKDEV
 MODULE_ALIAS_FS("cramfs");
+#endif
+#ifdef CONFIG_CRAMFS_PHYSMEM
+MODULE_ALIAS_FS("cramfs_physmem");
+#endif
 
 static int __init init_cramfs_fs(void)
 {
 	int rv;
 
-	rv = cramfs_uncompress_init();
-	if (rv < 0)
-		return rv;
-	rv = register_filesystem(&cramfs_fs_type);
-	if (rv < 0)
-		cramfs_uncompress_exit();
-	return rv;
+	if ((rv = cramfs_uncompress_init()) < 0)
+		goto err0;
+	if (IS_ENABLED(CONFIG_CRAMFS_BLOCKDEV) &&
+	    (rv = register_filesystem(&cramfs_fs_type)) < 0)
+		goto err1;
+	if (IS_ENABLED(CONFIG_CRAMFS_PHYSMEM) &&
+	    (rv = register_filesystem(&cramfs_physmem_fs_type)) < 0)
+		goto err2;
+	return 0;
+
+err2:	if (IS_ENABLED(CONFIG_CRAMFS_BLOCKDEV))
+		unregister_filesystem(&cramfs_fs_type);
+err1:	cramfs_uncompress_exit();
+err0:	return rv;
 }
 
 static void __exit exit_cramfs_fs(void)
 {
 	cramfs_uncompress_exit();
-	unregister_filesystem(&cramfs_fs_type);
+	if (IS_ENABLED(CONFIG_CRAMFS_BLOCKDEV))
+		unregister_filesystem(&cramfs_fs_type);
+	if (IS_ENABLED(CONFIG_CRAMFS_PHYSMEM))
+		unregister_filesystem(&cramfs_physmem_fs_type);
 }
 
 module_init(init_cramfs_fs)
-- 
2.9.5

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#1713216 — RE: [PATCH v2 1/5] cramfs: direct memory access support

On Wednesday, August 16, 2017, Nicolas Pitre wrote:
> Small embedded systems typically execute the kernel code in place (XIP)
> directly from flash to save on precious RAM usage. This adds the ability
> to consume filesystem data directly from flash to the cramfs filesystem
> as well. Cramfs is particularly well suited to this feature as it is
> very simple and its RAM usage is already very low, and with this feature
> it is possible to use it with no block device support and even lower RAM
> usage.
> 
> This patch was inspired by a similar patch from Shane Nay dated 17 years
> ago that used to be very popular in embedded circles but never made it
> into mainline. This is a cleaned-up implementation that uses far fewer
> memory address at run time when both methods are configured in. In the
> context of small IoT deployments, this functionality has become relevant
> and useful again.
> 
> To distinguish between both access types, the cramfs_physmem filesystem
> type must be specified when using a memory accessible cramfs image, and
> the physaddr argument must provide the actual filesystem image's physical
> memory location.
> 
> Signed-off-by: Nicolas Pitre <nico@linaro.org>
> ---
>  fs/cramfs/Kconfig |  30 ++++++-
>  fs/cramfs/inode.c | 264 +++++++++++++++++++++++++++++++++++++++++++------
> -----
>  2 files changed, 242 insertions(+), 52 deletions(-)
> 
> diff --git a/fs/cramfs/Kconfig b/fs/cramfs/Kconfig
> index 11b29d491b..5eed4ad2d5 100644
> --- a/fs/cramfs/Kconfig
> +++ b/fs/cramfs/Kconfig
> @@ -1,6 +1,5 @@
>  config CRAMFS
>  	tristate "Compressed ROM file system support (cramfs) (OBSOLETE)"
> -	depends on BLOCK
>  	select ZLIB_INFLATE
>  	help
>  	  Saying Y here includes support for CramFs (Compressed ROM File
> @@ -20,3 +19,32 @@ config CRAMFS
>  	  in terms of performance and features.
> 
>  	  If unsure, say N.
> +
> +config CRAMFS_BLOCKDEV
> +	bool "Support CramFs image over a regular block device" if EXPERT
> +	depends on CRAMFS && BLOCK
> +	default y
> +	help
> +	  This option allows the CramFs driver to load data from a regular
> +	  block device such a disk partition or a ramdisk.
> +


trailing whitespace


> +config CRAMFS_PHYSMEM
> +	bool "Support CramFs image directly mapped in physical memory"
> +	depends on CRAMFS
> +	default y if !CRAMFS_BLOCKDEV
> +	help
> +	  This option allows the CramFs driver to load data directly from
> +	  a linear adressed memory range (usually non volatile memory
> +	  like flash) instead of going through the block device layer.
> +	  This saves some memory since no intermediate buffering is
> +	  necessary.
> +
> +	  The filesystem type for this feature is "cramfs_physmem".
> +	  The location of the CramFs image in memory is board
> +	  dependent. Therefore, if you say Y, you must know the proper
> +	  physical address where to store the CramFs image and specify
> +	  it using the physaddr=0x******** mount option (for example:
> +	  "mount -t cramfs_physmem -o physaddr=0x100000 none /mnt").
> +
> +	  If unsure, say N.
> +


new blank line at EOF



-Chris

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#1713277 — RE: [PATCH v2 1/5] cramfs: direct memory access support

On Wed, 16 Aug 2017, Chris Brandt wrote:

> On Wednesday, August 16, 2017, Nicolas Pitre wrote:
> > +	bool "Support CramFs image over a regular block device" if EXPERT
> > +	depends on CRAMFS && BLOCK
> > +	default y
> > +	help
> > +	  This option allows the CramFs driver to load data from a regular
> > +	  block device such a disk partition or a ramdisk.
> > +
> 
> 
> trailing whitespace

Yeah... Fixed it and the others in my git repo, thanks.
This is something that can be done with git apply --whitespace=fix so I 
won't repost unless I get more comments.


Nicolas

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#1713187 — [PATCH v2 3/5] cramfs: implement uncompressed and arbitrary data block positioning

Two new capabilities are introduced here:

- The ability to store some blocks uncompressed.

- The ability to locate blocks anywhere.

Those capabilities can be used independently, but the combination
opens the possibility for execute-in-place (XIP) of program text segments
that must remain uncompressed, and in the MMU case, must have a specific
alignment.  It is even possible to still have the writable data segments
from the same file compressed as they have to be copied into RAM anyway.

This is achieved by giving special meanings to some unused block pointer
bits while remaining compatible with legacy cramfs images.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
---
 fs/cramfs/README               | 31 ++++++++++++++-
 fs/cramfs/inode.c              | 87 +++++++++++++++++++++++++++++++++---------
 include/uapi/linux/cramfs_fs.h | 20 +++++++++-
 3 files changed, 118 insertions(+), 20 deletions(-)

diff --git a/fs/cramfs/README b/fs/cramfs/README
index 9d4e7ea311..d71b27e0ff 100644
--- a/fs/cramfs/README
+++ b/fs/cramfs/README
@@ -49,17 +49,46 @@ same as the start of the (i+1)'th <block> if there is one).  The first
 <block> immediately follows the last <block_pointer> for the file.
 <block_pointer>s are each 32 bits long.
 
+When the CRAMFS_FLAG_EXT_BLOCK_POINTERS capability bit is set, each
+<block_pointer>'s top bits may contain special flags as follows:
+
+CRAMFS_BLK_FLAG_UNCOMPRESSED (bit 31):
+	The block data is not compressed and should be copied verbatim.
+
+CRAMFS_BLK_FLAG_DIRECT_PTR (bit 30):
+	The <block_pointer> stores the actual block start offset and not
+	its end, shifted right by 2 bits. The block must therefore be
+	aligned to a 4-byte boundary. The block size is either blksize
+	if CRAMFS_BLK_FLAG_UNCOMPRESSED is also specified, otherwise
+	the compressed data length is included in the first 2 bytes of
+	the block data. This is used to allow discontiguous data layout
+	and specific data block alignments e.g. for XIP applications.
+
+
 The order of <file_data>'s is a depth-first descent of the directory
 tree, i.e. the same order as `find -size +0 \( -type f -o -type l \)
 -print'.
 
 
 <block>: The i'th <block> is the output of zlib's compress function
-applied to the i'th blksize-sized chunk of the input data.
+applied to the i'th blksize-sized chunk of the input data if the
+corresponding CRAMFS_BLK_FLAG_UNCOMPRESSED <block_ptr> bit is not set,
+otherwise it is the input data directly.
 (For the last <block> of the file, the input may of course be smaller.)
 Each <block> may be a different size.  (See <block_pointer> above.)
+
 <block>s are merely byte-aligned, not generally u32-aligned.
 
+When CRAMFS_BLK_FLAG_DIRECT_PTR is specified then the corresponding
+<block> may be located anywhere and not necessarily contiguous with
+the previous/next blocks. In that case it is minimally u32-aligned.
+If CRAMFS_BLK_FLAG_UNCOMPRESSED is also specified then the size is always
+blksize except for the last block which is limited by the file length.
+If CRAMFS_BLK_FLAG_DIRECT_PTR is set and CRAMFS_BLK_FLAG_UNCOMPRESSED
+is not set then the first 2 bytes of the block contains the size of the
+remaining block data as this cannot be determined from the placement of
+logically adjacent blocks.
+
 
 Holes
 -----
diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index 393eb27ef4..b825ae162c 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -636,33 +636,84 @@ static int cramfs_readpage(struct file *file, struct page *page)
 	if (page->index < maxblock) {
 		struct super_block *sb = inode->i_sb;
 		u32 blkptr_offset = OFFSET(inode) + page->index*4;
-		u32 start_offset, compr_len;
+		u32 block_ptr, block_start, block_len;
+		bool uncompressed, direct;
 
-		start_offset = OFFSET(inode) + maxblock*4;
 		mutex_lock(&read_mutex);
-		if (page->index)
-			start_offset = *(u32 *) cramfs_read(sb, blkptr_offset-4,
-				4);
-		compr_len = (*(u32 *) cramfs_read(sb, blkptr_offset, 4) -
-			start_offset);
-		mutex_unlock(&read_mutex);
+		block_ptr = *(u32 *) cramfs_read(sb, blkptr_offset, 4);
+		uncompressed = (block_ptr & CRAMFS_BLK_FLAG_UNCOMPRESSED);
+		direct = (block_ptr & CRAMFS_BLK_FLAG_DIRECT_PTR);
+		block_ptr &= ~CRAMFS_BLK_FLAGS;
+
+		if (direct) {
+			/*
+			 * The block pointer is an absolute start pointer,
+			 * shifted by 2 bits. The size is included in the
+			 * first 2 bytes of the data block when compressed,
+			 * or PAGE_SIZE otherwise.
+			 */
+			block_start = block_ptr << 2;
+			if (uncompressed) {
+				block_len = PAGE_SIZE;
+				/* if last block: cap to file length */
+				if (page->index == maxblock - 1)
+					block_len = offset_in_page(inode->i_size);
+			} else {
+				block_len = *(u16 *)
+					cramfs_read(sb, block_start, 2);
+				block_start += 2;
+			}
+		} else {
+			/*
+			 * The block pointer indicates one past the end of
+			 * the current block (start of next block). If this
+			 * is the first block then it starts where the block
+			 * pointer table ends, otherwise its start comes
+			 * from the previous block's pointer.
+			 */
+			block_start = OFFSET(inode) + maxblock*4;
+			if (page->index)
+				block_start = *(u32 *)
+					cramfs_read(sb, blkptr_offset-4, 4);
+			/* Beware... previous ptr might be a direct ptr */
+			if (unlikely(block_start & CRAMFS_BLK_FLAG_DIRECT_PTR)) {
+				/* See comments on earlier code. */
+				u32 prev_start = block_start;
+			       block_start = prev_start & ~CRAMFS_BLK_FLAGS;
+			       block_start <<= 2;
+				if (prev_start & CRAMFS_BLK_FLAG_UNCOMPRESSED) {
+					block_start += PAGE_SIZE;
+				} else {
+					block_len = *(u16 *)
+						cramfs_read(sb, block_start, 2);
+					block_start += 2 + block_len;
+				}
+			}
+			block_start &= ~CRAMFS_BLK_FLAGS;
+			block_len = block_ptr - block_start;
+		}
 
-		if (compr_len == 0)
+		if (block_len == 0)
 			; /* hole */
-		else if (unlikely(compr_len > (PAGE_SIZE << 1))) {
-			pr_err("bad compressed blocksize %u\n",
-				compr_len);
+		else if (unlikely(block_len > 2*PAGE_SIZE ||
+				  (uncompressed && block_len > PAGE_SIZE))) {
+			mutex_unlock(&read_mutex);
+			pr_err("bad data blocksize %u\n", block_len);
 			goto err;
+		} else if (uncompressed) {
+			memcpy(pgdata,
+			       cramfs_read(sb, block_start, block_len),
+			       block_len);
+			bytes_filled = block_len;
 		} else {
-			mutex_lock(&read_mutex);
 			bytes_filled = cramfs_uncompress_block(pgdata,
 				 PAGE_SIZE,
-				 cramfs_read(sb, start_offset, compr_len),
-				 compr_len);
-			mutex_unlock(&read_mutex);
-			if (unlikely(bytes_filled < 0))
-				goto err;
+				 cramfs_read(sb, block_start, block_len),
+				 block_len);
 		}
+		mutex_unlock(&read_mutex);
+		if (unlikely(bytes_filled < 0))
+			goto err;
 	}
 
 	memset(pgdata + bytes_filled, 0, PAGE_SIZE - bytes_filled);
diff --git a/include/uapi/linux/cramfs_fs.h b/include/uapi/linux/cramfs_fs.h
index e4611a9b92..ed250aa372 100644
--- a/include/uapi/linux/cramfs_fs.h
+++ b/include/uapi/linux/cramfs_fs.h
@@ -73,6 +73,7 @@ struct cramfs_super {
 #define CRAMFS_FLAG_HOLES		0x00000100	/* support for holes */
 #define CRAMFS_FLAG_WRONG_SIGNATURE	0x00000200	/* reserved */
 #define CRAMFS_FLAG_SHIFTED_ROOT_OFFSET	0x00000400	/* shifted root fs */
+#define CRAMFS_FLAG_EXT_BLOCK_POINTERS	0x00000800	/* block pointer extensions */
 
 /*
  * Valid values in super.flags.  Currently we refuse to mount
@@ -82,7 +83,24 @@ struct cramfs_super {
 #define CRAMFS_SUPPORTED_FLAGS	( 0x000000ff \
 				| CRAMFS_FLAG_HOLES \
 				| CRAMFS_FLAG_WRONG_SIGNATURE \
-				| CRAMFS_FLAG_SHIFTED_ROOT_OFFSET )
+				| CRAMFS_FLAG_SHIFTED_ROOT_OFFSET \
+				| CRAMFS_FLAG_EXT_BLOCK_POINTERS )
 
+/*
+ * Block pointer flags
+ *
+ * The maximum block offset that needs to be represented is roughly:
+ * 
+ *   (1 << CRAMFS_OFFSET_WIDTH) * 4 +
+ *   (1 << CRAMFS_SIZE_WIDTH) / PAGE_SIZE * (4 + PAGE_SIZE)
+ *   = 0x11004000
+ *
+ * That leaves room for 3 flag bits in the block pointer table.
+ */
+#define CRAMFS_BLK_FLAG_UNCOMPRESSED	(1 << 31)
+#define CRAMFS_BLK_FLAG_DIRECT_PTR	(1 << 30)
+
+#define CRAMFS_BLK_FLAGS	( CRAMFS_BLK_FLAG_UNCOMPRESSED \
+				| CRAMFS_BLK_FLAG_DIRECT_PTR )
 
 #endif /* _UAPI__CRAMFS_H */
-- 
2.9.5

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#1713215 — RE: [PATCH v2 3/5] cramfs: implement uncompressed and arbitrary data block positioning

On Wednesday, August 16, 2017, Nicolas Pitre wrote:
> Two new capabilities are introduced here:
> 
> - The ability to store some blocks uncompressed.
> 
> - The ability to locate blocks anywhere.
> 
> Those capabilities can be used independently, but the combination
> opens the possibility for execute-in-place (XIP) of program text segments
> that must remain uncompressed, and in the MMU case, must have a specific
> alignment.  It is even possible to still have the writable data segments
> from the same file compressed as they have to be copied into RAM anyway.
> 
> This is achieved by giving special meanings to some unused block pointer
> bits while remaining compatible with legacy cramfs images.
> 
> Signed-off-by: Nicolas Pitre <nico@linaro.org>
> ---
>  fs/cramfs/README               | 31 ++++++++++++++-
>  fs/cramfs/inode.c              | 87 +++++++++++++++++++++++++++++++++----
> -----
>  include/uapi/linux/cramfs_fs.h | 20 +++++++++-
>  3 files changed, 118 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/cramfs/README b/fs/cramfs/README
> index 9d4e7ea311..d71b27e0ff 100644
> --- a/fs/cramfs/README
> +++ b/fs/cramfs/README
> @@ -49,17 +49,46 @@ same as the start of the (i+1)'th <block> if there is
> one).  The first
>  <block> immediately follows the last <block_pointer> for the file.
>  <block_pointer>s are each 32 bits long.
> 
> +When the CRAMFS_FLAG_EXT_BLOCK_POINTERS capability bit is set, each
> +<block_pointer>'s top bits may contain special flags as follows:
> +
> +CRAMFS_BLK_FLAG_UNCOMPRESSED (bit 31):
> +	The block data is not compressed and should be copied verbatim.
> +
> +CRAMFS_BLK_FLAG_DIRECT_PTR (bit 30):
> +	The <block_pointer> stores the actual block start offset and not
> +	its end, shifted right by 2 bits. The block must therefore be
> +	aligned to a 4-byte boundary. The block size is either blksize
> +	if CRAMFS_BLK_FLAG_UNCOMPRESSED is also specified, otherwise
> +	the compressed data length is included in the first 2 bytes of
> +	the block data. This is used to allow discontiguous data layout
> +	and specific data block alignments e.g. for XIP applications.
> +
> +
>  The order of <file_data>'s is a depth-first descent of the directory
>  tree, i.e. the same order as `find -size +0 \( -type f -o -type l \)
>  -print'.
> 
> 
>  <block>: The i'th <block> is the output of zlib's compress function
> -applied to the i'th blksize-sized chunk of the input data.
> +applied to the i'th blksize-sized chunk of the input data if the
> +corresponding CRAMFS_BLK_FLAG_UNCOMPRESSED <block_ptr> bit is not set,
> +otherwise it is the input data directly.
>  (For the last <block> of the file, the input may of course be smaller.)
>  Each <block> may be a different size.  (See <block_pointer> above.)
> +
>  <block>s are merely byte-aligned, not generally u32-aligned.
> 
> +When CRAMFS_BLK_FLAG_DIRECT_PTR is specified then the corresponding
> +<block> may be located anywhere and not necessarily contiguous with
> +the previous/next blocks. In that case it is minimally u32-aligned.
> +If CRAMFS_BLK_FLAG_UNCOMPRESSED is also specified then the size is always
> +blksize except for the last block which is limited by the file length.
> +If CRAMFS_BLK_FLAG_DIRECT_PTR is set and CRAMFS_BLK_FLAG_UNCOMPRESSED
> +is not set then the first 2 bytes of the block contains the size of the
> +remaining block data as this cannot be determined from the placement of
> +logically adjacent blocks.
> +
> 
>  Holes
>  -----
> diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
> index 393eb27ef4..b825ae162c 100644
> --- a/fs/cramfs/inode.c
> +++ b/fs/cramfs/inode.c
> @@ -636,33 +636,84 @@ static int cramfs_readpage(struct file *file, struct
> page *page)
>  	if (page->index < maxblock) {
>  		struct super_block *sb = inode->i_sb;
>  		u32 blkptr_offset = OFFSET(inode) + page->index*4;
> -		u32 start_offset, compr_len;
> +		u32 block_ptr, block_start, block_len;
> +		bool uncompressed, direct;
> 
> -		start_offset = OFFSET(inode) + maxblock*4;
>  		mutex_lock(&read_mutex);
> -		if (page->index)
> -			start_offset = *(u32 *) cramfs_read(sb, blkptr_offset-4,
> -				4);
> -		compr_len = (*(u32 *) cramfs_read(sb, blkptr_offset, 4) -
> -			start_offset);
> -		mutex_unlock(&read_mutex);
> +		block_ptr = *(u32 *) cramfs_read(sb, blkptr_offset, 4);
> +		uncompressed = (block_ptr & CRAMFS_BLK_FLAG_UNCOMPRESSED);
> +		direct = (block_ptr & CRAMFS_BLK_FLAG_DIRECT_PTR);
> +		block_ptr &= ~CRAMFS_BLK_FLAGS;
> +
> +		if (direct) {
> +			/*
> +			 * The block pointer is an absolute start pointer,
> +			 * shifted by 2 bits. The size is included in the
> +			 * first 2 bytes of the data block when compressed,
> +			 * or PAGE_SIZE otherwise.
> +			 */
> +			block_start = block_ptr << 2;
> +			if (uncompressed) {
> +				block_len = PAGE_SIZE;
> +				/* if last block: cap to file length */
> +				if (page->index == maxblock - 1)
> +					block_len = offset_in_page(inode->i_size);
> +			} else {
> +				block_len = *(u16 *)
> +					cramfs_read(sb, block_start, 2);
> +				block_start += 2;
> +			}
> +		} else {
> +			/*
> +			 * The block pointer indicates one past the end of
> +			 * the current block (start of next block). If this
> +			 * is the first block then it starts where the block
> +			 * pointer table ends, otherwise its start comes
> +			 * from the previous block's pointer.
> +			 */
> +			block_start = OFFSET(inode) + maxblock*4;
> +			if (page->index)
> +				block_start = *(u32 *)
> +					cramfs_read(sb, blkptr_offset-4, 4);
> +			/* Beware... previous ptr might be a direct ptr */
> +			if (unlikely(block_start & CRAMFS_BLK_FLAG_DIRECT_PTR))
> {
> +				/* See comments on earlier code. */
> +				u32 prev_start = block_start;
> +			       block_start = prev_start & ~CRAMFS_BLK_FLAGS;
> +			       block_start <<= 2;
> +				if (prev_start & CRAMFS_BLK_FLAG_UNCOMPRESSED) {
> +					block_start += PAGE_SIZE;
> +				} else {
> +					block_len = *(u16 *)
> +						cramfs_read(sb, block_start, 2);
> +					block_start += 2 + block_len;
> +				}
> +			}
> +			block_start &= ~CRAMFS_BLK_FLAGS;
> +			block_len = block_ptr - block_start;
> +		}
> 
> -		if (compr_len == 0)
> +		if (block_len == 0)
>  			; /* hole */
> -		else if (unlikely(compr_len > (PAGE_SIZE << 1))) {
> -			pr_err("bad compressed blocksize %u\n",
> -				compr_len);
> +		else if (unlikely(block_len > 2*PAGE_SIZE ||
> +				  (uncompressed && block_len > PAGE_SIZE))) {
> +			mutex_unlock(&read_mutex);
> +			pr_err("bad data blocksize %u\n", block_len);
>  			goto err;
> +		} else if (uncompressed) {
> +			memcpy(pgdata,
> +			       cramfs_read(sb, block_start, block_len),
> +			       block_len);
> +			bytes_filled = block_len;
>  		} else {
> -			mutex_lock(&read_mutex);
>  			bytes_filled = cramfs_uncompress_block(pgdata,
>  				 PAGE_SIZE,
> -				 cramfs_read(sb, start_offset, compr_len),
> -				 compr_len);
> -			mutex_unlock(&read_mutex);
> -			if (unlikely(bytes_filled < 0))
> -				goto err;
> +				 cramfs_read(sb, block_start, block_len),
> +				 block_len);
>  		}
> +		mutex_unlock(&read_mutex);
> +		if (unlikely(bytes_filled < 0))
> +			goto err;
>  	}
> 
>  	memset(pgdata + bytes_filled, 0, PAGE_SIZE - bytes_filled);
> diff --git a/include/uapi/linux/cramfs_fs.h
> b/include/uapi/linux/cramfs_fs.h
> index e4611a9b92..ed250aa372 100644
> --- a/include/uapi/linux/cramfs_fs.h
> +++ b/include/uapi/linux/cramfs_fs.h
> @@ -73,6 +73,7 @@ struct cramfs_super {
>  #define CRAMFS_FLAG_HOLES		0x00000100	/* support for holes */
>  #define CRAMFS_FLAG_WRONG_SIGNATURE	0x00000200	/* reserved */
>  #define CRAMFS_FLAG_SHIFTED_ROOT_OFFSET	0x00000400	/* shifted root fs
> */
> +#define CRAMFS_FLAG_EXT_BLOCK_POINTERS	0x00000800	/* block pointer
> extensions */
> 
>  /*
>   * Valid values in super.flags.  Currently we refuse to mount
> @@ -82,7 +83,24 @@ struct cramfs_super {
>  #define CRAMFS_SUPPORTED_FLAGS	( 0x000000ff \
>  				| CRAMFS_FLAG_HOLES \
>  				| CRAMFS_FLAG_WRONG_SIGNATURE \
> -				| CRAMFS_FLAG_SHIFTED_ROOT_OFFSET )
> +				| CRAMFS_FLAG_SHIFTED_ROOT_OFFSET \
> +				| CRAMFS_FLAG_EXT_BLOCK_POINTERS )
> 
> +/*
> + * Block pointer flags
> + *
> + * The maximum block offset that needs to be represented is roughly:
> + * 


trailing whitespace


-Chris

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