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-rw-r--r--fs/cramfs/README31
-rw-r--r--fs/cramfs/inode.c90
-rw-r--r--include/uapi/linux/cramfs_fs.h26
3 files changed, 126 insertions, 21 deletions
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 <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 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 */
generated by cgit v1.2.3-55-g7522 (git 2.39.0) at 2024-06-17 02:18:44 +0200