[Virtio-fs] [PATCH v2 1/2][RFC] virtiofsd: virtiofsd: add definition of fuse_buf_writev()

[Dr. David Alan Gilbert]

* piaojun (piaojun at huawei.com) wrote:
> Define fuse_buf_writev() which use pwritev and writev to improve io
> bandwidth.
> 
> Signed-off-by: Jun Piao <piaojun at huawei.com>
> Suggested-by: Dr. David Alan Gilbert <dgilbert at redhat.com>
> ---
>  contrib/virtiofsd/buffer.c      | 37 +++++++++++++++++++++++++++++++++++++
>  contrib/virtiofsd/fuse_common.h | 14 ++++++++++++++
>  contrib/virtiofsd/seccomp.c     |  2 ++
>  3 files changed, 53 insertions(+)
> 
> diff --git a/contrib/virtiofsd/buffer.c b/contrib/virtiofsd/buffer.c
> index 655be137..642830f 100644
> --- a/contrib/virtiofsd/buffer.c
> +++ b/contrib/virtiofsd/buffer.c
> @@ -15,6 +15,7 @@
>  #include <unistd.h>
>  #include <errno.h>
>  #include <assert.h>
> +#include <stdlib.h>
> 
>  size_t fuse_buf_size(const struct fuse_bufvec *bufv)
>  {
> @@ -71,6 +72,42 @@ static ssize_t fuse_buf_write(const struct fuse_buf *dst, size_t dst_off,
>  	return copied;
>  }
> 
> +ssize_t fuse_buf_writev(fuse_req_t req,
> +			     struct fuse_bufvec *out_buf,
> +			     struct fuse_bufvec *in_buf,
> +			     enum fuse_buf_copy_flags flags)
> +{
> +	ssize_t res, i, buf_index, iovcnt;
> +	struct iovec * iov;
> +	int fd = out_buf->buf[0].fd;
> +	off_t pos = out_buf->buf[0].pos;

That's again assuming that the 'pos' in subsequent elements of out_buf
is sequential; is it?
What about any other flags on in_buf?

> +	if (in_buf->count > 2)
> +		iovcnt = in_buf->count - 1;
> +	else
> +		iovcnt = 1;
> +
> +	iov = malloc(iovcnt * sizeof(struct iovec));

You could use calloc.

> +	if (!iov)
> +		return -ENOMEM;
> +
> +	for (i = 0, buf_index = 1; i < iovcnt; i++, buf_index++) {
> +		iov[i].iov_base = in_buf->buf[buf_index].mem;
> +		iov[i].iov_len = in_buf->buf[buf_index].size;
> +	}
> +
> +	if (flags & FUSE_BUF_FD_SEEK)
> +		res = pwritev(fd, iov, iovcnt, pos);
> +	else
> +		res = writev(fd, iov, iovcnt);
> +
> +	if (res == -1 || res == 0)
> +		res = -errno;

Does errno get set on a res == 0 ?

Dave

> +	free(iov);
> +	return res;
> +}
> +
>  static ssize_t fuse_buf_read(const struct fuse_buf *dst, size_t dst_off,
>  			     const struct fuse_buf *src, size_t src_off,
>  			     size_t len)
> diff --git a/contrib/virtiofsd/fuse_common.h b/contrib/virtiofsd/fuse_common.h
> index 001e6d6..7c07da7 100644
> --- a/contrib/virtiofsd/fuse_common.h
> +++ b/contrib/virtiofsd/fuse_common.h
> @@ -730,6 +730,20 @@ ssize_t fuse_buf_copy(fuse_req_t req,
>  		      enum fuse_buf_copy_flags flags);
> 
>  /**
> + * Write data from one buffer vector to another
> + *
> + * @param req The request this copy is part of
> + * @param out_buf destination buffer vector
> + * @param in_buf source buffer vector
> + * @param flags flags controlling the copy
> + * @return actual number of bytes written or -errno on error
> + */
> +ssize_t fuse_buf_writev(fuse_req_t req,
> +		      struct fuse_bufvec *out_buf,
> +		      struct fuse_bufvec *in_buf,
> +		      enum fuse_buf_copy_flags flags);
> +
> +/**
>   * Memory buffer iterator
>   *
>   */
> diff --git a/contrib/virtiofsd/seccomp.c b/contrib/virtiofsd/seccomp.c
> index 5f1c873..4bba30b 100644
> --- a/contrib/virtiofsd/seccomp.c
> +++ b/contrib/virtiofsd/seccomp.c
> @@ -60,6 +60,7 @@ static const int syscall_whitelist[] = {
>  	SCMP_SYS(ppoll),
>  	SCMP_SYS(prctl), /* TODO restrict to just PR_SET_NAME? */
>  	SCMP_SYS(preadv),
> +	SCMP_SYS(pwritev),
>  	SCMP_SYS(pwrite64),
>  	SCMP_SYS(read),
>  	SCMP_SYS(readlinkat),
> @@ -78,6 +79,7 @@ static const int syscall_whitelist[] = {
>  	SCMP_SYS(unlinkat),
>  	SCMP_SYS(utimensat),
>  	SCMP_SYS(write),
> +	SCMP_SYS(writev),
>  };
> 
>  /* Syscalls used when --syslog is enabled */
> -- 
--
Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK