From 99c18ce580c6cc6763e694b4ce320d7b226ab59b Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Fri, 13 Oct 2017 16:09:23 -0400 Subject: 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 patch adds to cramfs the ability to consume filesystem data directly from flash as well. Cramfs is particularly well suited to this feature as it is very simple with low RAM usage, and with this feature it is possible to use it with no block device support and consequently 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 ifdef's and gets the actual memory location for the filesystem image via MTD at run time. In the context of small IoT deployments, this functionality has become relevant and useful again. Signed-off-by: Nicolas Pitre Tested-by: Chris Brandt Reviewed-by: Christoph Hellwig Signed-off-by: Al Viro --- fs/cramfs/Kconfig | 30 +++++++- fs/cramfs/inode.c | 212 +++++++++++++++++++++++++++++++++++++++++++----------- 2 files changed, 199 insertions(+), 43 deletions(-) (limited to 'fs/cramfs') diff --git a/fs/cramfs/Kconfig b/fs/cramfs/Kconfig index 11b29d491b7c..ef86b06bc064 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_MTD + bool "Support CramFs image directly mapped in physical memory" + depends on CRAMFS && MTD + 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 location of the CramFs image is determined by a + MTD device capable of direct memory mapping e.g. from + the 'physmap' map driver or a resulting MTD partition. + For example, this would mount the cramfs image stored in + the MTD partition named "xip_fs" on the /mnt mountpoint: + + mount -t cramfs mtd:xip_fs /mnt + + If unsure, say N. diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c index 7919967488cb..bcdccb7a820b 100644 --- a/fs/cramfs/inode.c +++ b/fs/cramfs/inode.c @@ -19,6 +19,8 @@ #include #include #include +#include +#include #include #include #include @@ -36,6 +38,9 @@ struct cramfs_sb_info { unsigned long blocks; unsigned long files; unsigned long flags; + void *linear_virt_addr; + resource_size_t linear_phys_addr; + size_t mtd_point_size; }; static inline struct cramfs_sb_info *CRAMFS_SB(struct super_block *sb) @@ -140,6 +145,9 @@ 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 +168,10 @@ 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 to 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]; @@ -239,11 +247,49 @@ static void *cramfs_read(struct super_block *sb, unsigned int offset, unsigned i return read_buffers[buffer] + offset; } +/* + * 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_MTD) && 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_kill_sb(struct super_block *sb) { struct cramfs_sb_info *sbi = CRAMFS_SB(sb); - kill_block_super(sb); + if (IS_ENABLED(CCONFIG_CRAMFS_MTD) && sb->s_mtd) { + if (sbi && sbi->mtd_point_size) + mtd_unpoint(sb->s_mtd, 0, sbi->mtd_point_size); + kill_mtd_super(sb); + } else if (IS_ENABLED(CONFIG_CRAMFS_BLOCKDEV) && sb->s_bdev) { + kill_block_super(sb); + } kfree(sbi); } @@ -254,34 +300,24 @@ 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 +325,12 @@ 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 |= 0555; - 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); @@ -347,10 +394,79 @@ 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_mtd_fill_super(struct super_block *sb, void *data, + int silent) +{ + struct cramfs_sb_info *sbi; + struct cramfs_super super; + int err; + + sbi = kzalloc(sizeof(struct cramfs_sb_info), GFP_KERNEL); + if (!sbi) + return -ENOMEM; + sb->s_fs_info = sbi; + + /* Map only one page for now. Will remap it when fs size is known. */ + err = mtd_point(sb->s_mtd, 0, PAGE_SIZE, &sbi->mtd_point_size, + &sbi->linear_virt_addr, &sbi->linear_phys_addr); + if (err || sbi->mtd_point_size != PAGE_SIZE) { + pr_err("unable to get direct memory access to mtd:%s\n", + sb->s_mtd->name); + return err ? : -ENODATA; + } + + pr_info("checking physical address %pap for linear cramfs image\n", + &sbi->linear_phys_addr); + err = cramfs_read_super(sb, &super, silent); + if (err) + return err; + + /* Remap the whole filesystem now */ + pr_info("linear cramfs image on mtd:%s appears to be %lu KB in size\n", + sb->s_mtd->name, sbi->size/1024); + mtd_unpoint(sb->s_mtd, 0, PAGE_SIZE); + err = mtd_point(sb->s_mtd, 0, sbi->size, &sbi->mtd_point_size, + &sbi->linear_virt_addr, &sbi->linear_phys_addr); + if (err || sbi->mtd_point_size != sbi->size) { + pr_err("unable to get direct memory access to mtd:%s\n", + sb->s_mtd->name); + return err ? : -ENODATA; + } + + return cramfs_finalize_super(sb, &super.root); +} + static int cramfs_statfs(struct dentry *dentry, struct kstatfs *buf) { struct super_block *sb = dentry->d_sb; - u64 id = huge_encode_dev(sb->s_bdev->bd_dev); + u64 id = 0; + + if (sb->s_bdev) + id = huge_encode_dev(sb->s_bdev->bd_dev); + else if (sb->s_dev) + id = huge_encode_dev(sb->s_dev); buf->f_type = CRAMFS_MAGIC; buf->f_bsize = PAGE_SIZE; @@ -573,10 +689,22 @@ 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_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); + struct dentry *ret = ERR_PTR(-ENOPROTOOPT); + + if (IS_ENABLED(CONFIG_CRAMFS_MTD)) { + ret = mount_mtd(fs_type, flags, dev_name, data, + cramfs_mtd_fill_super); + if (!IS_ERR(ret)) + return ret; + } + if (IS_ENABLED(CONFIG_CRAMFS_BLOCKDEV)) { + ret = mount_bdev(fs_type, flags, dev_name, data, + cramfs_blkdev_fill_super); + } + return ret; } static struct file_system_type cramfs_fs_type = { -- cgit v1.2.3 From fd4f6f2a78aeaebb7094c1bb9b30623d18a86e4c Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Thu, 12 Oct 2017 02:16:11 -0400 Subject: 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 Tested-by: Chris Brandt Signed-off-by: Al Viro --- fs/cramfs/README | 31 ++++++++++++++- fs/cramfs/inode.c | 90 +++++++++++++++++++++++++++++++++--------- include/uapi/linux/cramfs_fs.h | 26 +++++++++++- 3 files changed, 126 insertions(+), 21 deletions(-) (limited to 'fs/cramfs') diff --git a/fs/cramfs/README b/fs/cramfs/README index 9d4e7ea311f4..d71b27e0ff15 100644 --- a/fs/cramfs/README +++ b/fs/cramfs/README @@ -49,17 +49,46 @@ same as the start of the (i+1)'th if there is one). The first immediately follows the last for the file. s are each 32 bits long. +When the CRAMFS_FLAG_EXT_BLOCK_POINTERS capability bit is set, each +'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 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 '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'. : The i'th 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 bit is not set, +otherwise it is the input data directly. (For the last of the file, the input may of course be smaller.) Each may be a different size. (See above.) + s are merely byte-aligned, not generally u32-aligned. +When CRAMFS_BLK_FLAG_DIRECT_PTR is specified then the corresponding + 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 bcdccb7a820b..19045453a8f3 100644 --- a/fs/cramfs/inode.c +++ b/fs/cramfs/inode.c @@ -618,34 +618,86 @@ 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 blkptr_offset = OFFSET(inode) + page->index * 4; + 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 << CRAMFS_BLK_DIRECT_PTR_SHIFT; + 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 <<= CRAMFS_BLK_DIRECT_PTR_SHIFT; + 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 e4611a9b9243..ce2c885133e2 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 +83,30 @@ 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 ) + +/* + * Direct blocks are at least 4-byte aligned. + * Pointers to direct blocks are shifted down by 2 bits. + */ +#define CRAMFS_BLK_DIRECT_PTR_SHIFT 2 #endif /* _UAPI__CRAMFS_H */ -- cgit v1.2.3 From eddcd97659e31f59fc99c6c3ca3dcce403585f7e Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Thu, 12 Oct 2017 02:16:12 -0400 Subject: cramfs: add mmap support When cramfs in physical memory is used then we have the opportunity to map files directly from ROM, directly into user space, saving on RAM usage. This gives us Execute-In-Place (XIP) support. For a file to be mmap()-able, the map area has to correspond to a range of uncompressed and contiguous blocks, and in the MMU case it also has to be page aligned. A version of mkcramfs with appropriate support is necessary to create such a filesystem image. In the MMU case it may happen for a vma structure to extend beyond the actual file size. This is notably the case in binfmt_elf.c:elf_map(). Or the file's last block is shared with other files and cannot be mapped as is. Rather than refusing to mmap it, we do a "mixed" map and let the regular fault handler populate the unmapped area with RAM-backed pages. In practice the unmapped area is seldom accessed so page faults might never occur before this area is discarded. In the non-MMU case it is the get_unmapped_area method that is responsible for providing the address where the actual data can be found. No mapping is necessary of course. Signed-off-by: Nicolas Pitre Tested-by: Chris Brandt Signed-off-by: Al Viro --- fs/cramfs/inode.c | 209 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 209 insertions(+) (limited to 'fs/cramfs') diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c index 19045453a8f3..9a2ab419ba62 100644 --- a/fs/cramfs/inode.c +++ b/fs/cramfs/inode.c @@ -15,7 +15,10 @@ #include #include +#include #include +#include +#include #include #include #include @@ -51,6 +54,7 @@ static inline struct cramfs_sb_info *CRAMFS_SB(struct super_block *sb) static const struct super_operations cramfs_ops; static const struct inode_operations cramfs_dir_inode_operations; static const struct file_operations cramfs_directory_operations; +static const struct file_operations cramfs_physmem_fops; static const struct address_space_operations cramfs_aops; static DEFINE_MUTEX(read_mutex); @@ -98,6 +102,10 @@ static struct inode *get_cramfs_inode(struct super_block *sb, case S_IFREG: inode->i_fop = &generic_ro_fops; inode->i_data.a_ops = &cramfs_aops; + if (IS_ENABLED(CONFIG_CRAMFS_MTD) && + CRAMFS_SB(sb)->flags & CRAMFS_FLAG_EXT_BLOCK_POINTERS && + CRAMFS_SB(sb)->linear_phys_addr) + inode->i_fop = &cramfs_physmem_fops; break; case S_IFDIR: inode->i_op = &cramfs_dir_inode_operations; @@ -279,6 +287,207 @@ static void *cramfs_read(struct super_block *sb, unsigned int offset, return NULL; } +/* + * For a mapping to be possible, we need a range of uncompressed and + * contiguous blocks. Return the offset for the first block and number of + * valid blocks for which that is true, or zero otherwise. + */ +static u32 cramfs_get_block_range(struct inode *inode, u32 pgoff, u32 *pages) +{ + struct cramfs_sb_info *sbi = CRAMFS_SB(inode->i_sb); + int i; + u32 *blockptrs, first_block_addr; + + /* + * We can dereference memory directly here as this code may be + * reached only when there is a direct filesystem image mapping + * available in memory. + */ + blockptrs = (u32 *)(sbi->linear_virt_addr + OFFSET(inode) + pgoff * 4); + first_block_addr = blockptrs[0] & ~CRAMFS_BLK_FLAGS; + i = 0; + do { + u32 block_off = i * (PAGE_SIZE >> CRAMFS_BLK_DIRECT_PTR_SHIFT); + u32 expect = (first_block_addr + block_off) | + CRAMFS_BLK_FLAG_DIRECT_PTR | + CRAMFS_BLK_FLAG_UNCOMPRESSED; + if (blockptrs[i] != expect) { + pr_debug("range: block %d/%d got %#x expects %#x\n", + pgoff+i, pgoff + *pages - 1, + blockptrs[i], expect); + if (i == 0) + return 0; + break; + } + } while (++i < *pages); + + *pages = i; + return first_block_addr << CRAMFS_BLK_DIRECT_PTR_SHIFT; +} + +#ifdef CONFIG_MMU + +/* + * Return true if the last page of a file in the filesystem image contains + * some other data that doesn't belong to that file. It is assumed that the + * last block is CRAMFS_BLK_FLAG_DIRECT_PTR | CRAMFS_BLK_FLAG_UNCOMPRESSED + * (verified by cramfs_get_block_range() and directly accessible in memory. + */ +static bool cramfs_last_page_is_shared(struct inode *inode) +{ + struct cramfs_sb_info *sbi = CRAMFS_SB(inode->i_sb); + u32 partial, last_page, blockaddr, *blockptrs; + char *tail_data; + + partial = offset_in_page(inode->i_size); + if (!partial) + return false; + last_page = inode->i_size >> PAGE_SHIFT; + blockptrs = (u32 *)(sbi->linear_virt_addr + OFFSET(inode)); + blockaddr = blockptrs[last_page] & ~CRAMFS_BLK_FLAGS; + blockaddr <<= CRAMFS_BLK_DIRECT_PTR_SHIFT; + tail_data = sbi->linear_virt_addr + blockaddr + partial; + return memchr_inv(tail_data, 0, PAGE_SIZE - partial) ? true : false; +} + +static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma) +{ + struct inode *inode = file_inode(file); + struct cramfs_sb_info *sbi = CRAMFS_SB(inode->i_sb); + unsigned int pages, max_pages, offset; + unsigned long address, pgoff = vma->vm_pgoff; + char *bailout_reason; + int ret; + + ret = generic_file_readonly_mmap(file, vma); + if (ret) + return ret; + + /* + * Now try to pre-populate ptes for this vma with a direct + * mapping avoiding memory allocation when possible. + */ + + /* Could COW work here? */ + bailout_reason = "vma is writable"; + if (vma->vm_flags & VM_WRITE) + goto bailout; + + max_pages = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT; + bailout_reason = "beyond file limit"; + if (pgoff >= max_pages) + goto bailout; + pages = min(vma_pages(vma), max_pages - pgoff); + + offset = cramfs_get_block_range(inode, pgoff, &pages); + bailout_reason = "unsuitable block layout"; + if (!offset) + goto bailout; + address = sbi->linear_phys_addr + offset; + bailout_reason = "data is not page aligned"; + if (!PAGE_ALIGNED(address)) + goto bailout; + + /* Don't map the last page if it contains some other data */ + if (pgoff + pages == max_pages && cramfs_last_page_is_shared(inode)) { + pr_debug("mmap: %s: last page is shared\n", + file_dentry(file)->d_name.name); + pages--; + } + + if (!pages) { + bailout_reason = "no suitable block remaining"; + goto bailout; + } + + if (pages == vma_pages(vma)) { + /* + * The entire vma is mappable. remap_pfn_range() will + * make it distinguishable from a non-direct mapping + * in /proc//maps by substituting the file offset + * with the actual physical address. + */ + ret = remap_pfn_range(vma, vma->vm_start, address >> PAGE_SHIFT, + pages * PAGE_SIZE, vma->vm_page_prot); + } else { + /* + * Let's create a mixed map if we can't map it all. + * The normal paging machinery will take care of the + * unpopulated ptes via cramfs_readpage(). + */ + int i; + vma->vm_flags |= VM_MIXEDMAP; + for (i = 0; i < pages && !ret; i++) { + unsigned long off = i * PAGE_SIZE; + pfn_t pfn = phys_to_pfn_t(address + off, PFN_DEV); + ret = vm_insert_mixed(vma, vma->vm_start + off, pfn); + } + } + + if (!ret) + pr_debug("mapped %s[%lu] at 0x%08lx (%u/%lu pages) " + "to vma 0x%08lx, page_prot 0x%llx\n", + file_dentry(file)->d_name.name, pgoff, + address, pages, vma_pages(vma), vma->vm_start, + (unsigned long long)pgprot_val(vma->vm_page_prot)); + return ret; + +bailout: + pr_debug("%s[%lu]: direct mmap impossible: %s\n", + file_dentry(file)->d_name.name, pgoff, bailout_reason); + /* Didn't manage any direct map, but normal paging is still possible */ + return 0; +} + +#else /* CONFIG_MMU */ + +static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma) +{ + return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS; +} + +static unsigned long cramfs_physmem_get_unmapped_area(struct file *file, + unsigned long addr, unsigned long len, + unsigned long pgoff, unsigned long flags) +{ + struct inode *inode = file_inode(file); + struct super_block *sb = inode->i_sb; + struct cramfs_sb_info *sbi = CRAMFS_SB(sb); + unsigned int pages, block_pages, max_pages, offset; + + pages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT; + max_pages = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT; + if (pgoff >= max_pages || pages > max_pages - pgoff) + return -EINVAL; + block_pages = pages; + offset = cramfs_get_block_range(inode, pgoff, &block_pages); + if (!offset || block_pages != pages) + return -ENOSYS; + addr = sbi->linear_phys_addr + offset; + pr_debug("get_unmapped for %s ofs %#lx siz %lu at 0x%08lx\n", + file_dentry(file)->d_name.name, pgoff*PAGE_SIZE, len, addr); + return addr; +} + +static unsigned int cramfs_physmem_mmap_capabilities(struct file *file) +{ + return NOMMU_MAP_COPY | NOMMU_MAP_DIRECT | + NOMMU_MAP_READ | NOMMU_MAP_EXEC; +} + +#endif /* CONFIG_MMU */ + +static const struct file_operations cramfs_physmem_fops = { + .llseek = generic_file_llseek, + .read_iter = generic_file_read_iter, + .splice_read = generic_file_splice_read, + .mmap = cramfs_physmem_mmap, +#ifndef CONFIG_MMU + .get_unmapped_area = cramfs_physmem_get_unmapped_area, + .mmap_capabilities = cramfs_physmem_mmap_capabilities, +#endif +}; + static void cramfs_kill_sb(struct super_block *sb) { struct cramfs_sb_info *sbi = CRAMFS_SB(sb); -- cgit v1.2.3 From 8d59598c35dc1071e6c36f86c9a95f26dd08b4e5 Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Thu, 12 Oct 2017 02:16:13 -0400 Subject: cramfs: rehabilitate it Update documentation, pointer to latest tools, appoint myself as maintainer. Given it's been unloved for so long, I don't expect anyone will protest. Signed-off-by: Nicolas Pitre Tested-by: Chris Brandt Signed-off-by: Al Viro --- Documentation/filesystems/cramfs.txt | 42 ++++++++++++++++++++++++++++++++++++ MAINTAINERS | 4 ++-- fs/cramfs/Kconfig | 9 +++++--- 3 files changed, 50 insertions(+), 5 deletions(-) (limited to 'fs/cramfs') diff --git a/Documentation/filesystems/cramfs.txt b/Documentation/filesystems/cramfs.txt index 4006298f6707..8e19a53d648b 100644 --- a/Documentation/filesystems/cramfs.txt +++ b/Documentation/filesystems/cramfs.txt @@ -45,6 +45,48 @@ you can just change the #define in mkcramfs.c, so long as you don't mind the filesystem becoming unreadable to future kernels. +Memory Mapped cramfs image +-------------------------- + +The CRAMFS_MTD Kconfig option adds support for loading data directly from +a physical linear 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 to hold the data before +decompressing. + +And when data blocks are kept uncompressed and properly aligned, they will +automatically be mapped directly into user space whenever possible providing +eXecute-In-Place (XIP) from ROM of read-only segments. Data segments mapped +read-write (hence they have to be copied to RAM) may still be compressed in +the cramfs image in the same file along with non compressed read-only +segments. Both MMU and no-MMU systems are supported. This is particularly +handy for tiny embedded systems with very tight memory constraints. + +The location of the cramfs image in memory is system dependent. You must +know the proper physical address where the cramfs image is located and +configure an MTD device for it. Also, that MTD device must be supported +by a map driver that implements the "point" method. Examples of such +MTD drivers are cfi_cmdset_0001 (Intel/Sharp CFI flash) or physmap +(Flash device in physical memory map). MTD partitions based on such devices +are fine too. Then that device should be specified with the "mtd:" prefix +as the mount device argument. For example, to mount the MTD device named +"fs_partition" on the /mnt directory: + +$ mount -t cramfs mtd:fs_partition /mnt + +To boot a kernel with this as root filesystem, suffice to specify +something like "root=mtd:fs_partition" on the kernel command line. + + +Tools +----- + +A version of mkcramfs that can take advantage of the latest capabilities +described above can be found here: + +https://github.com/npitre/cramfs-tools + + For /usr/share/magic -------------------- diff --git a/MAINTAINERS b/MAINTAINERS index 2d3d750b19c0..3438aaa20b73 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -3676,8 +3676,8 @@ F: drivers/cpuidle/* F: include/linux/cpuidle.h CRAMFS FILESYSTEM -W: http://sourceforge.net/projects/cramfs/ -S: Orphan / Obsolete +M: Nicolas Pitre +S: Maintained F: Documentation/filesystems/cramfs.txt F: fs/cramfs/ diff --git a/fs/cramfs/Kconfig b/fs/cramfs/Kconfig index ef86b06bc064..f937082f3244 100644 --- a/fs/cramfs/Kconfig +++ b/fs/cramfs/Kconfig @@ -1,5 +1,5 @@ config CRAMFS - tristate "Compressed ROM file system support (cramfs) (OBSOLETE)" + tristate "Compressed ROM file system support (cramfs)" select ZLIB_INFLATE help Saying Y here includes support for CramFs (Compressed ROM File @@ -15,8 +15,11 @@ config CRAMFS cramfs. Note that the root file system (the one containing the directory /) cannot be compiled as a module. - This filesystem is obsoleted by SquashFS, which is much better - in terms of performance and features. + This filesystem is limited in capabilities and performance on + purpose to remain small and low on RAM usage. It is most suitable + for small embedded systems. If you have ample RAM to spare, you may + consider a more capable compressed filesystem such as SquashFS + which is much better in terms of performance and features. If unsure, say N. -- cgit v1.2.3