On 8/21/20 3:38 AM, Omar Sandoval wrote:

From: Omar Sandoval <redacted>

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 <redacted>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef