ext4: correctly calculate number of blocks for fiemap (aca92ff6) · Commits · 戴 / test

ext4_fiemap() rounds the length of the requested range down to blocksize, which is is not the true number of blocks that cover the requested region. This problem is especially impressive if the user requests only the first byte of a file: not a single extent will be reported. We fix this by calculating the last block of the region and then subtract to find the number of blocks in the extents. Signed-off-by:

Leonard Michlmayr <leonard.michlmayr@gmail.com> Signed-off-by:

"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/extents.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -3768,7 +3768,6 @@ int ext4_fiemap(struct inode inode, struct fiemap_extent_info fieinfo,
		__u64 start, __u64 len)
		{
		ext4_lblk_t start_blk;
		ext4_lblk_t len_blks;
		int error = 0;

		/* fallback to generic here if not in extents fmt */
		@@ -3782,8 +3781,14 @@ int ext4_fiemap(struct inode inode, struct fiemap_extent_info fieinfo,
		if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR) {
		error = ext4_xattr_fiemap(inode, fieinfo);
		} else {
		ext4_lblk_t len_blks;
		__u64 last_blk;

		start_blk = start >> inode->i_sb->s_blocksize_bits;
		len_blks = len >> inode->i_sb->s_blocksize_bits;
		last_blk = (start + len - 1) >> inode->i_sb->s_blocksize_bits;
		if (last_blk >= EXT_MAX_BLOCK)
		last_blk = EXT_MAX_BLOCK-1;
		len_blks = ((ext4_lblk_t) last_blk) - start_blk + 1;

		/*
		* Walk the extent tree gathering extent information.

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