[PATCH 2/3] sunrpc: simplify xdr_partial_copy_from_skb

Christoph Hellwig
2025-05-15T11:49:23Z

csum_partial_copy_to_xdr can handle a checksumming and non-checksumming
case and implements this using a callback, which leads to a lot of
boilerplate code and indirect calls in the fast path.

Switch to storing a need_checksum flag in struct xdr_skb_reader instead
to remove the indirect call and simplify the code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
net/sunrpc/socklib.c | 163 ++++++++++++++++---------------------------
1 file changed, 59 insertions(+), 104 deletions(-)

diff --git a/net/sunrpc/socklib.c b/net/sunrpc/socklib.c
index 1b2b84feeec6..75e31e3a3ced 100644
--- a/net/sunrpc/socklib.c
+++ b/net/sunrpc/socklib.c
@@ -27,97 +27,60 @@
struct xdr_skb_reader {
struct sk_buff *skb;
unsigned int offset;
+ bool need_checksum;
size_t count;
__wsum csum;
};

-typedef size_t (*xdr_skb_read_actor)(struct xdr_skb_reader *desc, void *to,
- size_t len);
-
/**
* xdr_skb_read_bits - copy some data bits from skb to internal buffer
* @desc: sk_buff copy helper
* @to: copy destination
* @len: number of bytes to copy
*
- * Possibly called several times to iterate over an sk_buff and copy
- * data out of it.
+ * Possibly called several times to iterate over an sk_buff and copy data out of
+ * it.
*/
static size_t
xdr_skb_read_bits(struct xdr_skb_reader *desc, void *to, size_t len)
{
- if (len > desc->count)
- len = desc->count;
- if (unlikely(skb_copy_bits(desc->skb, desc->offset, to, len)))
- return 0;
- desc->count -= len;
- desc->offset += len;
- return len;
-}
+ len = min(len, desc->count);
+
+ if (desc->need_checksum) {
+ __wsum csum;
+
+ csum = skb_copy_and_csum_bits(desc->skb, desc->offset, to, len);
+ desc->csum = csum_block_add(desc->csum, csum, desc->offset);
+ } else {
+ if (unlikely(skb_copy_bits(desc->skb, desc->offset, to, len)))
+ return 0;
+ }

-/**
- * xdr_skb_read_and_csum_bits - copy and checksum from skb to buffer
- * @desc: sk_buff copy helper
- * @to: copy destination
- * @len: number of bytes to copy
- *
- * Same as skb_read_bits, but calculate a checksum at the same time.
- */
-static size_t xdr_skb_read_and_csum_bits(struct xdr_skb_reader *desc, void *to, size_t len)
-{
- unsigned int pos;
- __wsum csum2;
-
- if (len > desc->count)
- len = desc->count;
- pos = desc->offset;
- csum2 = skb_copy_and_csum_bits(desc->skb, pos, to, len);
- desc->csum = csum_block_add(desc->csum, csum2, pos);
desc->count -= len;
desc->offset += len;
return len;
}

-/**
- * xdr_partial_copy_from_skb - copy data out of an skb
- * @xdr: target XDR buffer
- * @base: starting offset
- * @desc: sk_buff copy helper
- * @copy_actor: virtual method for copying data
- *
- */
static ssize_t
-xdr_partial_copy_from_skb(struct xdr_buf *xdr, unsigned int base, struct xdr_skb_reader *desc, xdr_skb_read_actor copy_actor)
+xdr_partial_copy_from_skb(struct xdr_buf *xdr, struct xdr_skb_reader *desc)
{
- struct page **ppage = xdr->pages;
- unsigned int len, pglen = xdr->page_len;
- ssize_t copied = 0;
- size_t ret;
-
- len = xdr->head[0].iov_len;
- if (base < len) {
- len -= base;
- ret = copy_actor(desc, (char *)xdr->head[0].iov_base + base, len);
- copied += ret;
- if (ret != len || !desc->count)
- goto out;
- base = 0;
- } else
- base -= len;
-
- if (unlikely(pglen == 0))
- goto copy_tail;
- if (unlikely(base >= pglen)) {
- base -= pglen;
- goto copy_tail;
- }
- if (base || xdr->page_base) {
- pglen -= base;
- base += xdr->page_base;
- ppage += base >> PAGE_SHIFT;
- base &= ~PAGE_MASK;
- }
- do {
+ struct page **ppage = xdr->pages + (xdr->page_base >> PAGE_SHIFT);
+ unsigned int poff = xdr->page_base & ~PAGE_MASK;
+ unsigned int pglen = xdr->page_len;
+ ssize_t copied = 0;
+ size_t ret;
+
+ if (xdr->head[0].iov_len == 0)
+ return 0;
+
+ ret = xdr_skb_read_bits(desc, xdr->head[0].iov_base,
+ xdr->head[0].iov_len);
+ if (ret != xdr->head[0].iov_len || !desc->count)
+ return ret;
+ copied += ret;
+
+ while (pglen) {
+ unsigned int len = min(PAGE_SIZE - poff, pglen);
char *kaddr;

/* ACL likes to be lazy in allocating pages - ACLs
@@ -126,36 +89,29 @@ xdr_partial_copy_from_skb(struct xdr_buf *xdr, unsigned int base, struct xdr_skb
*ppage = alloc_page(GFP_NOWAIT | __GFP_NOWARN);
if (unlikely(*ppage == NULL)) {
if (copied == 0)
- copied = -ENOMEM;
- goto out;
+ return -ENOMEM;
+ return copied;
}
}

- len = PAGE_SIZE;
kaddr = kmap_atomic(*ppage);
- if (base) {
- len -= base;
- if (pglen < len)
- len = pglen;
- ret = copy_actor(desc, kaddr + base, len);
- base = 0;
- } else {
- if (pglen < len)
- len = pglen;
- ret = copy_actor(desc, kaddr, len);
- }
+ ret = xdr_skb_read_bits(desc, kaddr + poff, len);
flush_dcache_page(*ppage);
kunmap_atomic(kaddr);
+
copied += ret;
if (ret != len || !desc->count)
- goto out;
+ return copied;
ppage++;
- } while ((pglen -= len) != 0);
-copy_tail:
- len = xdr->tail[0].iov_len;
- if (base < len)
- copied += copy_actor(desc, (char *)xdr->tail[0].iov_base + base, len - base);
-out:
+ pglen -= len;
+ poff = 0;
+ }
+
+ if (xdr->tail[0].iov_len) {
+ copied += xdr_skb_read_bits(desc, xdr->tail[0].iov_base,
+ xdr->tail[0].iov_len);
+ }
+
return copied;
}

@@ -169,17 +125,22 @@ xdr_partial_copy_from_skb(struct xdr_buf *xdr, unsigned int base, struct xdr_skb
*/
int csum_partial_copy_to_xdr(struct xdr_buf *xdr, struct sk_buff *skb)
{
- struct xdr_skb_reader desc;
-
- desc.skb = skb;
- desc.offset = 0;
- desc.count = skb->len - desc.offset;
+ struct xdr_skb_reader desc = {
+ .skb = skb,
+ .count = skb->len - desc.offset,
+ };

- if (skb_csum_unnecessary(skb))
- goto no_checksum;
+ if (skb_csum_unnecessary(skb)) {
+ if (xdr_partial_copy_from_skb(xdr, &desc) < 0)
+ return -1;
+ if (desc.count)
+ return -1;
+ return 0;
+ }

+ desc.need_checksum = true;
desc.csum = csum_partial(skb->data, desc.offset, skb->csum);
- if (xdr_partial_copy_from_skb(xdr, 0, &desc, xdr_skb_read_and_csum_bits) < 0)
+ if (xdr_partial_copy_from_skb(xdr, &desc) < 0)
return -1;
if (desc.offset != skb->len) {
__wsum csum2;
@@ -194,12 +155,6 @@ int csum_partial_copy_to_xdr(struct xdr_buf *xdr, struct sk_buff *skb)
!skb->csum_complete_sw)
netdev_rx_csum_fault(skb->dev, skb);
return 0;
-no_checksum:
- if (xdr_partial_copy_from_skb(xdr, 0, &desc, xdr_skb_read_bits) < 0)
- return -1;
- if (desc.count)
- return -1;
- return 0;
}
EXPORT_SYMBOL_GPL(csum_partial_copy_to_xdr);

--
2.47.2