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| author | Nicolas Pitre <nicolas.pitre@linaro.org> | 2017-10-12 09:16:11 +0300 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2017-10-15 07:47:22 +0300 |
| commit | fd4f6f2a78aeaebb7094c1bb9b30623d18a86e4c (patch) | |
| tree | cf6e32f1d7207c0cd63fb606ae5510a1bd5f39f7 /include/uapi/linux/cramfs_fs.h | |
| parent | 99c18ce580c6cc6763e694b4ce320d7b226ab59b (diff) | |
| download | linux-fd4f6f2a78aeaebb7094c1bb9b30623d18a86e4c.tar.xz | |
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>
Tested-by: Chris Brandt <chris.brandt@renesas.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'include/uapi/linux/cramfs_fs.h')
| -rw-r--r-- | include/uapi/linux/cramfs_fs.h | 26 |
1 files changed, 25 insertions, 1 deletions
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 */ |