Am 16.09.2010 20:54, schrieb Laurent Vivier:
> This patch allows to reduce the boot time from an NBD server from 225 seconds
> to
> 5 seconds (time between the "boot cd:0" and the kernel init) for the
> following command lines:
>
> ./qemu-nbd -t ../ISO/debian-500-powerpc-netinst.iso
> and
> ./ppc-softmmu/qemu-system-ppc -cdrom nbd:localhost:1024
>
> Signed-off-by: Laurent Vivier <laur...@vivier.eu>
I agree with Stefan. It's good to have a description of the results in
the commit message, but describing what has actually changed from a
technical perspective would be helpful, too.
> ---
> nbd.c | 20 +++++++++++++++-----
> 1 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/nbd.c b/nbd.c
> index 011b50f..5d7c758 100644
> --- a/nbd.c
> +++ b/nbd.c
> @@ -655,7 +655,7 @@ int nbd_trip(BlockDriverState *bs, int csock, off_t size,
> uint64_t dev_offset,
> if (nbd_receive_request(csock, &request) == -1)
> return -1;
>
> - if (request.len > data_size) {
> + if (request.len + sizeof(struct nbd_reply) > data_size) {
> LOG("len (%u) is larger than max len (%u)",
> request.len, data_size);
> errno = EINVAL;
> @@ -687,7 +687,8 @@ int nbd_trip(BlockDriverState *bs, int csock, off_t size,
> uint64_t dev_offset,
> case NBD_CMD_READ:
> TRACE("Request type is READ");
>
> - if (bdrv_read(bs, (request.from + dev_offset) / 512, data,
> + if (bdrv_read(bs, (request.from + dev_offset) / 512,
> + data + sizeof(struct nbd_reply),
> request.len / 512) == -1) {
> LOG("reading from file failed");
> errno = EINVAL;
> @@ -697,12 +698,21 @@ int nbd_trip(BlockDriverState *bs, int csock, off_t
> size, uint64_t dev_offset,
>
> TRACE("Read %u byte(s)", request.len);
>
> - if (nbd_send_reply(csock, &reply) == -1)
> - return -1;
> + /* Reply
> + [ 0 .. 3] magic (NBD_REPLY_MAGIC)
> + [ 4 .. 7] error (0 == no error)
> + [ 7 .. 15] handle
> + */
> +
> + cpu_to_be32w((uint32_t*)data, NBD_REPLY_MAGIC);
> + cpu_to_be32w((uint32_t*)(data + 4), reply.error);
> + cpu_to_be64w((uint64_t*)(data + 8), reply.handle);
Hm, if I understand this right, you rely on the compiler padding out
structs here. You reserved sizeof(struct nbd_reply) bytes and the struct
is defined like this:
struct nbd_reply {
uint32_t error;
uint64_t handle;
};
So isn't it pure luck that the compiler does the right thing and gives
you 16 bytes? If you want to use the struct for this, you should add a
uint32_t magic to it and make it packed.
Kevin
