2011/8/29 Jeff Layton <jlayton@xxxxxxxxxx>:
> Eventually we'll want to allow cifsd to read data directly into the
> pagecache. In order to do that we'll need a routine that can take a
> kvec array and pass that directly to kernel_recvmsg.
>
> Unfortunately though, the kernel's recvmsg routines modify the kvec
> array that gets passed in, so we need to use a copy of the kvec array
> and refresh that copy on each pass through the loop.
>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> fs/cifs/connect.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 files changed, 65 insertions(+), 7 deletions(-)
>
> diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
> index e6da201..08c6b0e 100644
> --- a/fs/cifs/connect.c
> +++ b/fs/cifs/connect.c
> @@ -375,14 +375,58 @@ server_unresponsive(struct TCP_Server_Info *server)
> return false;
> }
>
> +/*
> + * kvec_array_setup - clone a kvec array, and advance into it
> + * @new: pointer to memory for cloned array
> + * @iov: pointer to original array
> + * @nr_segs: number of members in original array
> + * @bytes: number of bytes to advance into the cloned array
> + *
> + * This function will copy the array provided in iov to a section of memory
> + * and advance the specified number of bytes into the new array. It returns
> + * the number of segments in the new array. "new" must be at least as big as
> + * the original iov array.
> + */
> +static unsigned int
> +kvec_array_init(struct kvec *new, struct kvec *iov, unsigned int nr_segs,
I think it should be kvec_array_setup as it said in the description above.
> + size_t bytes)
> +{
> + size_t base = 0;
> +
> + while (bytes || !iov->iov_len) {
> + int copy = min(bytes, iov->iov_len);
> +
> + bytes -= copy;
> + base += copy;
> + if (iov->iov_len == base) {
> + iov++;
> + nr_segs--;
> + base = 0;
> + }
> + }
> + memcpy(new, iov, sizeof(*iov) * nr_segs);
> + new->iov_base += base;
> + new->iov_len -= base;
> + return nr_segs;
> +}
> +
> static int
> -read_from_socket(struct TCP_Server_Info *server, char *buf,
> - unsigned int to_read)
> +readv_from_socket(struct TCP_Server_Info *server, struct kvec *iov_orig,
> + unsigned int nr_segs, unsigned int to_read)
> {
> int length = 0;
> int total_read;
> + unsigned int segs;
> struct msghdr smb_msg;
> - struct kvec iov;
> + struct kvec *iov;
> +
> + /*
> + * FIXME: allocation here may cause deadlocks under memory pressure.
> + * Switch this to use a fixed, per-socket buffer.
> + */
> + iov = kmalloc(sizeof(*iov_orig) * nr_segs, GFP_KERNEL);
> + if (!iov)
> + return -ENOMEM;
>
> smb_msg.msg_control = NULL;
> smb_msg.msg_controllen = 0;
> @@ -393,10 +437,11 @@ read_from_socket(struct TCP_Server_Info *server, char *buf,
> break;
> }
>
> - iov.iov_base = buf + total_read;
> - iov.iov_len = to_read;
> - length = kernel_recvmsg(server->ssocket, &smb_msg, &iov, 1,
> - to_read, 0);
> + segs = kvec_array_init(iov, iov_orig, nr_segs, total_read);
> +
> + length = kernel_recvmsg(server->ssocket, &smb_msg,
> + iov, segs, to_read, 0);
> +
> if (server->tcpStatus == CifsExiting) {
> total_read = -ESHUTDOWN;
> break;
> @@ -423,9 +468,22 @@ read_from_socket(struct TCP_Server_Info *server, char *buf,
> break;
> }
> }
> + kfree(iov);
> return total_read;
> }
>
> +static int
> +read_from_socket(struct TCP_Server_Info *server, char *buf,
> + unsigned int to_read)
> +{
> + struct kvec iov;
> +
> + iov.iov_base = buf;
> + iov.iov_len = to_read;
> +
> + return readv_from_socket(server, &iov, 1, to_read);
> +}
> +
> static bool
> check_rfc1002_header(struct TCP_Server_Info *server, char *buf)
> {
> --
> 1.7.6
>
> --
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--
Best regards,
Pavel Shilovsky.
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