Use RawFile as backend instead of File. This allows us to abstract
the access to the actual image with a specialized layer, so we have a
place where we can deal with the low-level peculiarities.
Signed-off-by: Sergio Lopez <slp@redhat.com>
Doing I/O on an image opened with O_DIRECT requires to adhere to
certain restrictions, requiring the following elements to be aligned:
- Address of the source/destination memory buffer.
- File offset.
- Length of the data to be read/written.
The actual alignment value depends on various elements, and according
to open(2) "(...) there is currently no filesystem-independent
interface for an application to discover these restrictions (...)".
To discover such value, we iterate through a list of alignments
(currently, 512 and 4096) calling pread() with each one and checking
if the operation succeeded.
We also extend RawFile so it can be used as a backend for QcowFile,
so the later can be easily adapted to support O_DIRECT too.
Signed-off-by: Sergio Lopez <slp@redhat.com>
The current backend only support rw, and we also need
add readonly support.
The new command:
vhost_user_blk \
--backend "image=/home/test.img, \
sock=/home/path/vhost.socket, \
readonly=true"
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Create a vhost-user-blk backend using vhost-user-backend and following
the conventions established by the existing vhost-user-net
implementation.
This backend is based on https://github.com/slp/vhost-user-backend,
but a bit simplified, making it closer to the original implementation
in Firecracker. The main features missing are EVENT_IDX, support for
asynchronous I/O and multiqueue, but it's still fully functional and
provides a good starting point for evolving it into a more complete
implementation.
Signed-off-by: Sergio Lopez <slp@redhat.com>
