Re: [PATCH] cifs: use discard iterator to discard unneeded network data more efficiently

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lightly updated patch


On Thu, Feb 25, 2021 at 1:29 PM Steve French <smfrench@xxxxxxxxx> wrote:
>
> The other two routines initialize in iov_iter_bvec
>
> iov->type
> iov->bvec
> iov->offset
> iov->count
>
> but iov_iter_discard already does the initialization:
> iov_type
> iov_offset
> iov_count
>
> and then we call cifs_readv_from_socket in all 3
> which sets:
>     iov->msg_control = NULL
>     iov->msg_controllen = NULL
>
> I will set the two additional ones to null
>     iov->msg_name
> and
>     iov->msg_namelen
>
>
>
> On Thu, Feb 4, 2021 at 4:29 AM Aurélien Aptel <aaptel@xxxxxxxx> wrote:
> >
> > Steve French <smfrench@xxxxxxxxx> writes:
> > > +ssize_t
> > > +cifs_discard_from_socket(struct TCP_Server_Info *server, size_t to_read)
> > > +{
> > > +     struct msghdr smb_msg;
> > > +
> > > +     iov_iter_discard(&smb_msg.msg_iter, READ, to_read);
> > > +
> > > +     return cifs_readv_from_socket(server, &smb_msg);
> > > +}
> > > +
> >
> > Shouldn't smb_msg be initialized to zeroes? Looking around this needs to
> > be done for cifs_read_from_socket() and cifs_read_page_from_socket() too.
> >
> > Cheers,
> > --
> > Aurélien Aptel / SUSE Labs Samba Team
> > GPG: 1839 CB5F 9F5B FB9B AA97  8C99 03C8 A49B 521B D5D3
> > SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg, DE
> > GF: Felix Imendörffer, Mary Higgins, Sri Rasiah HRB 247165 (AG München)
> >
>
>
> --
> Thanks,
>
> Steve



-- 
Thanks,

Steve
From 1b0bdb5e6c9c8846ab4a548093a32311ae9d0037 Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@xxxxxxxxxx>
Date: Thu, 4 Feb 2021 00:15:21 -0600
Subject: [PATCH] cifs: use discard iterator to discard unneeded network data
 more efficiently

The iterator, ITER_DISCARD, that can only be used in READ mode and
just discards any data copied to it, was added to allow a network
filesystem to discard any unwanted data sent by a server.
Convert cifs_discard_from_socket() to use this.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
---
 fs/cifs/cifsproto.h |  2 ++
 fs/cifs/cifssmb.c   |  6 +++---
 fs/cifs/connect.c   | 17 +++++++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
index d4b2cc7e6b1e..64eb5c817712 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -232,6 +232,8 @@ extern unsigned int setup_special_user_owner_ACE(struct cifs_ace *pace);
 extern void dequeue_mid(struct mid_q_entry *mid, bool malformed);
 extern int cifs_read_from_socket(struct TCP_Server_Info *server, char *buf,
 			         unsigned int to_read);
+extern ssize_t cifs_discard_from_socket(struct TCP_Server_Info *server,
+					size_t to_read);
 extern int cifs_read_page_from_socket(struct TCP_Server_Info *server,
 					struct page *page,
 					unsigned int page_offset,
diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index 0496934feecb..c279527aae92 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -1451,9 +1451,9 @@ cifs_discard_remaining_data(struct TCP_Server_Info *server)
 	while (remaining > 0) {
 		int length;
 
-		length = cifs_read_from_socket(server, server->bigbuf,
-				min_t(unsigned int, remaining,
-				    CIFSMaxBufSize + MAX_HEADER_SIZE(server)));
+		length = cifs_discard_from_socket(server,
+				min_t(size_t, remaining,
+				      CIFSMaxBufSize + MAX_HEADER_SIZE(server)));
 		if (length < 0)
 			return length;
 		server->total_read += length;
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 55b1ec731d52..b9085625334e 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -564,6 +564,23 @@ cifs_read_from_socket(struct TCP_Server_Info *server, char *buf,
 	return cifs_readv_from_socket(server, &smb_msg);
 }
 
+ssize_t
+cifs_discard_from_socket(struct TCP_Server_Info *server, size_t to_read)
+{
+	struct msghdr smb_msg;
+
+	/*
+	 *  iov_iter_discard already sets smb_msg.type and count and iov_offset
+	 *  and cifs_readv_from_socket sets msg_control and msg_controllen
+	 *  so little to initialize in struct msghdr
+	 */
+	smb_msg.msg_name = NULL;
+	smb_msg_namelen = 0;
+	iov_iter_discard(&smb_msg.msg_iter, READ, to_read);
+
+	return cifs_readv_from_socket(server, &smb_msg);
+}
+
 int
 cifs_read_page_from_socket(struct TCP_Server_Info *server, struct page *page,
 	unsigned int page_offset, unsigned int to_read)
-- 
2.27.0


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