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

Steve French
2021-02-25T21:05:15Z

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Had a typo in the previous attachment - reattached

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@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
---
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.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)

On Thu, Feb 25, 2021 at 1:43 PM Steve French <smfrench@gmail.com> wrote:
>
> lightly updated patch
>
>
> On Thu, Feb 25, 2021 at 1:29 PM Steve French <smfrench@gmail.com> 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@suse.com> wrote:
> > >
> > > Steve French <smfrench@gmail.com> 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

--
Thanks,

Steve

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From 1b0bdb5e6c9c8846ab4a548093a32311ae9d0037 Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Thu, 4 Feb 2021 00:15:21 -0600
Subject: [PATCH 1/2] 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@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
---
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.msg_namelen = 0;