Re: [bpf-next PATCH 04/16] net: generalize sk_alloc_sg to work with scatterlist rings

[David Miller]

From: John Fastabend 
Date: Mon, 05 Mar 2018 11:51:17 -0800

> The current implementation of sk_alloc_sg expects scatterlist to always
> start at entry 0 and complete at entry MAX_SKB_FRAGS.
> 
> Future patches will want to support starting at arbitrary offset into
> scatterlist so add an additional sg_start parameters and then default
> to the current values in TLS code paths.
> 
> Signed-off-by: John Fastabend 

Acked-by: David S. Miller 

[bpf-next PATCH 04/16] net: generalize sk_alloc_sg to work with scatterlist rings

[John Fastabend]

The current implementation of sk_alloc_sg expects scatterlist to always
start at entry 0 and complete at entry MAX_SKB_FRAGS.

Future patches will want to support starting at arbitrary offset into
scatterlist so add an additional sg_start parameters and then default
to the current values in TLS code paths.

Signed-off-by: John Fastabend 
---
 include/net/sock.h |2 +-
 net/core/sock.c|   27 ---
 net/tls/tls_sw.c   |4 ++--
 3 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 447150c..b7c75e0 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2142,7 +2142,7 @@ static inline struct page_frag *sk_page_frag(struct sock 
*sk)
 bool sk_page_frag_refill(struct sock *sk, struct page_frag *pfrag);
 
 int sk_alloc_sg(struct sock *sk, int len, struct scatterlist *sg,
-   int *sg_num_elem, unsigned int *sg_size,
+   int sg_start, int *sg_curr, unsigned int *sg_size,
int first_coalesce);
 
 /*
diff --git a/net/core/sock.c b/net/core/sock.c
index 4bda3e9..d14f64b 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2239,19 +2239,20 @@ bool sk_page_frag_refill(struct sock *sk, struct 
page_frag *pfrag)
 EXPORT_SYMBOL(sk_page_frag_refill);
 
 int sk_alloc_sg(struct sock *sk, int len, struct scatterlist *sg,
-   int *sg_num_elem, unsigned int *sg_size,
+   int sg_start, int *sg_curr_index, unsigned int *sg_curr_size,
int first_coalesce)
 {
+   int sg_curr = *sg_curr_index, use = 0, rc = 0;
+   unsigned int size = *sg_curr_size;
struct page_frag *pfrag;
-   unsigned int size = *sg_size;
-   int num_elem = *sg_num_elem, use = 0, rc = 0;
struct scatterlist *sge;
-   unsigned int orig_offset;
 
len -= size;
pfrag = sk_page_frag(sk);
 
while (len > 0) {
+   unsigned int orig_offset;
+
if (!sk_page_frag_refill(sk, pfrag)) {
rc = -ENOMEM;
goto out;
@@ -2269,17 +2270,21 @@ int sk_alloc_sg(struct sock *sk, int len, struct 
scatterlist *sg,
orig_offset = pfrag->offset;
pfrag->offset += use;
 
-   sge = sg + num_elem - 1;
-   if (num_elem > first_coalesce && sg_page(sg) == pfrag->page &&
+   sge = sg + sg_curr - 1;
+   if (sg_curr > first_coalesce && sg_page(sg) == pfrag->page &&
sg->offset + sg->length == orig_offset) {
sg->length += use;
} else {
-   sge++;
+   sge = sg + sg_curr;
sg_unmark_end(sge);
sg_set_page(sge, pfrag->page, use, orig_offset);
get_page(pfrag->page);
-   ++num_elem;
-   if (num_elem == MAX_SKB_FRAGS) {
+   sg_curr++;
+
+   if (sg_curr == MAX_SKB_FRAGS)
+   sg_curr = 0;
+
+   if (sg_curr == sg_start) {
rc = -ENOSPC;
break;
}
@@ -2288,8 +2293,8 @@ int sk_alloc_sg(struct sock *sk, int len, struct 
scatterlist *sg,
len -= use;
}
 out:
-   *sg_size = size;
-   *sg_num_elem = num_elem;
+   *sg_curr_size = size;
+   *sg_curr_index = sg_curr;
return rc;
 }
 EXPORT_SYMBOL(sk_alloc_sg);
diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 0fc8a24..057a558 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -94,7 +94,7 @@ static int alloc_encrypted_sg(struct sock *sk, int len)
int rc = 0;
 
rc = sk_alloc_sg(sk, len,
-ctx->sg_encrypted_data,
+ctx->sg_encrypted_data, 0,
 >sg_encrypted_num_elem,
 >sg_encrypted_size, 0);
 
@@ -107,7 +107,7 @@ static int alloc_plaintext_sg(struct sock *sk, int len)
struct tls_sw_context *ctx = tls_sw_ctx(tls_ctx);
int rc = 0;
 
-   rc = sk_alloc_sg(sk, len, ctx->sg_plaintext_data,
+   rc = sk_alloc_sg(sk, len, ctx->sg_plaintext_data, 0,
 >sg_plaintext_num_elem, >sg_plaintext_size,
 tls_ctx->pending_open_record_frags);