On 8/21/20 3:38 AM, Omar Sandoval wrote:
From: Omar Sandoval <osandov@xxxxxx> Btrfs supports transparent compression: data written by the user can be compressed when written to disk and decompressed when read back. However, we'd like to add an interface to write pre-compressed data directly to the filesystem, and the matching interface to read compressed data without decompressing it. This adds support for so-called "encoded I/O" via preadv2() and pwritev2(). A new RWF_ENCODED flags indicates that a read or write is "encoded". If this flag is set, iov[0].iov_base points to a struct encoded_iov which is used for metadata: namely, the compression algorithm, unencoded (i.e., decompressed) length, and what subrange of the unencoded data should be used (needed for truncated or hole-punched extents and when reading in the middle of an extent). For reads, the filesystem returns this information; for writes, the caller provides it to the filesystem. iov[0].iov_len must be set to sizeof(struct encoded_iov), which can be used to extend the interface in the future a la copy_struct_from_user(). The remaining iovecs contain the encoded extent. This adds the VFS helpers for supporting encoded I/O and documentation for filesystem support. Signed-off-by: Omar Sandoval <osandov@xxxxxx>
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx> Thanks, Josef
