[PATCH 5/8] fs: ext4: rely on _fs_read() to handle leading unaligned block read

[Qu Wenruo]

Just add ext4_get_blocksize() and a new assert() in ext4fs_read_file().

Signed-off-by: Qu Wenruo <wqu at suse.com>
---
Several cleanup candicate:

1. ext_fs->blksz is never populated, thus it's always 0
   We can not easily grab blocksize just like btrfs in this case.

   Thus we have to go the same calculation in ext4fs_read_file().

2. can not easily cleanup @skipfirst in ext4fs_read_file()
   It seems to screw up with soft link read.
---
 fs/ext4/ext4fs.c | 22 ++++++++++++++++++++++
 fs/fs.c          |  2 +-
 include/ext4fs.h |  1 +
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/ext4fs.c b/fs/ext4/ext4fs.c
index 4c89152ce4ad..b0568e77a895 100644
--- a/fs/ext4/ext4fs.c
+++ b/fs/ext4/ext4fs.c
@@ -69,6 +69,8 @@ int ext4fs_read_file(struct ext2fs_node *node, loff_t pos,
 	short status;
 	struct ext_block_cache cache;
 
+	assert(IS_ALIGNED(pos, blocksize));
+
 	ext_cache_init(&cache);
 
 	/* Adjust len so it we can't read past the end of the file. */
@@ -259,6 +261,26 @@ int ext4_read_file(const char *filename, void *buf, loff_t offset, loff_t len,
 	return ext4fs_read(buf, offset, len, len_read);
 }
 
+int ext4_get_blocksize(const char *filename)
+{
+	struct ext_filesystem *fs;
+	int log2blksz;
+	int log2_fs_blocksize;
+	loff_t file_len;
+	int ret;
+
+	ret = ext4fs_open(filename, &file_len);
+	if (ret < 0) {
+		printf("** File not found %s **\n", filename);
+		return -1;
+	}
+	fs = get_fs();
+	log2blksz = fs->dev_desc->log2blksz;
+	log2_fs_blocksize = LOG2_BLOCK_SIZE(ext4fs_file->data) - log2blksz;
+
+	return (1 << (log2_fs_blocksize + log2blksz));
+}
+
 int ext4fs_uuid(char *uuid_str)
 {
 	if (ext4fs_root == NULL)
diff --git a/fs/fs.c b/fs/fs.c
index f9df8d9ec9a4..3cd2c88a4895 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -236,7 +236,7 @@ static struct fstype_info fstypes[] = {
 		.exists = ext4fs_exists,
 		.size = ext4fs_size,
 		.read = ext4_read_file,
-		.get_blocksize = fs_get_blocksize_unsupported,
+		.get_blocksize = ext4_get_blocksize,
 #ifdef CONFIG_CMD_EXT4_WRITE
 		.write = ext4_write_file,
 		.ln = ext4fs_create_link,
diff --git a/include/ext4fs.h b/include/ext4fs.h
index cb5d9cc0a5c0..0f4cf32dcc2a 100644
--- a/include/ext4fs.h
+++ b/include/ext4fs.h
@@ -161,6 +161,7 @@ int ext4fs_probe(struct blk_desc *fs_dev_desc,
 		 struct disk_partition *fs_partition);
 int ext4_read_file(const char *filename, void *buf, loff_t offset, loff_t len,
 		   loff_t *actread);
+int ext4_get_blocksize(const char *filename);
 int ext4_read_superblock(char *buffer);
 int ext4fs_uuid(char *uuid_str);
 void ext_cache_init(struct ext_block_cache *cache);
-- 
2.36.1