head_cnt is a global variable which tracks how many entries in head[] are
currently used. The fact that it's global obscures the fact that the
lifetime over which it has a meaningful value is quite short: a single
call to of tcp_vu_data_from_sock().
Make it a local to tcp_vu_data_from_sock() to make that lifetime clearer.
We keep the head[] array global for now - although technically it has the
same valid lifetime - because it's large enough we might not want to put
it on the stack.
Cc: Laurent Vivier <lvivier(a)redhat.com>
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
tcp_vu.c | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)
diff --git a/tcp_vu.c b/tcp_vu.c
index 0622f173..6891ed13 100644
--- a/tcp_vu.c
+++ b/tcp_vu.c
@@ -38,7 +38,6 @@
static struct iovec iov_vu[VIRTQUEUE_MAX_SIZE + 1];
static struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE];
static int head[VIRTQUEUE_MAX_SIZE + 1];
-static int head_cnt;
/**
* tcp_vu_hdrlen() - return the size of the header in level 2 frame (TCP)
@@ -183,7 +182,7 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn,
int flags)
static ssize_t tcp_vu_sock_recv(const struct ctx *c,
const struct tcp_tap_conn *conn, bool v6,
uint32_t already_sent, size_t fillsize,
- int *iov_cnt)
+ int *iov_cnt, int *head_cnt)
{
struct vu_dev *vdev = c->vdev;
struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
@@ -202,7 +201,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c,
vu_init_elem(elem, &iov_vu[1], VIRTQUEUE_MAX_SIZE);
elem_cnt = 0;
- head_cnt = 0;
+ *head_cnt = 0;
while (fillsize > 0 && elem_cnt < VIRTQUEUE_MAX_SIZE) {
struct iovec *iov;
size_t frame_size, dlen;
@@ -221,7 +220,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c,
ASSERT(iov->iov_len >= hdrlen);
iov->iov_base = (char *)iov->iov_base + hdrlen;
iov->iov_len -= hdrlen;
- head[head_cnt++] = elem_cnt;
+ head[(*head_cnt)++] = elem_cnt;
fillsize -= dlen;
elem_cnt += cnt;
@@ -261,17 +260,18 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c,
len -= iov->iov_len;
}
/* adjust head count */
- while (head_cnt > 0 && head[head_cnt - 1] >= i)
- head_cnt--;
+ while (*head_cnt > 0 && head[*head_cnt - 1] >= i)
+ (*head_cnt)--;
+
/* mark end of array */
- head[head_cnt] = i;
+ head[*head_cnt] = i;
*iov_cnt = i;
/* release unused buffers */
vu_queue_rewind(vq, elem_cnt - i);
/* restore space for headers in iov */
- for (i = 0; i < head_cnt; i++) {
+ for (i = 0; i < *head_cnt; i++) {
struct iovec *iov = &elem[head[i]].in_sg[0];
iov->iov_base = (char *)iov->iov_base - hdrlen;
@@ -357,11 +357,11 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn
*conn)
struct vu_dev *vdev = c->vdev;
struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
ssize_t len, previous_dlen;
+ int i, iov_cnt, head_cnt;
size_t hdrlen, fillsize;
int v6 = CONN_V6(conn);
uint32_t already_sent;
const uint16_t *check;
- int i, iov_cnt;
if (!vu_queue_enabled(vq) || !vu_queue_started(vq)) {
debug("Got packet, but RX virtqueue not usable yet");
@@ -396,7 +396,8 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn
*conn)
/* collect the buffers from vhost-user and fill them with the
* data from the socket
*/
- len = tcp_vu_sock_recv(c, conn, v6, already_sent, fillsize, &iov_cnt);
+ len = tcp_vu_sock_recv(c, conn, v6, already_sent, fillsize,
+ &iov_cnt, &head_cnt);
if (len < 0) {
if (len != -EAGAIN && len != -EWOULDBLOCK) {
tcp_rst(c, conn);
--
2.48.1
On 18/02/2025 03:50, David Gibson wrote:head_cnt is a global variable which tracks how many entries in head[] are currently used. The fact that it's global obscures the fact that the lifetime over which it has a meaningful value is quite short: a single call to of tcp_vu_data_from_sock(). Make it a local to tcp_vu_data_from_sock() to make that lifetime clearer. We keep the head[] array global for now - although technically it has the same valid lifetime - because it's large enough we might not want to put it on the stack.We can make the array local but on the heap using a static declaration in the function. Reviewed-by: Laurent Vivier <lvivier(a)redhat.com>Cc: Laurent Vivier <lvivier(a)redhat.com> Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au> --- tcp_vu.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-) diff --git a/tcp_vu.c b/tcp_vu.c index 0622f173..6891ed13 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -38,7 +38,6 @@ static struct iovec iov_vu[VIRTQUEUE_MAX_SIZE + 1]; static struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE]; static int head[VIRTQUEUE_MAX_SIZE + 1]; -static int head_cnt; /** * tcp_vu_hdrlen() - return the size of the header in level 2 frame (TCP) @@ -183,7 +182,7 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) static ssize_t tcp_vu_sock_recv(const struct ctx *c, const struct tcp_tap_conn *conn, bool v6, uint32_t already_sent, size_t fillsize, - int *iov_cnt) + int *iov_cnt, int *head_cnt) { struct vu_dev *vdev = c->vdev; struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE]; @@ -202,7 +201,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, vu_init_elem(elem, &iov_vu[1], VIRTQUEUE_MAX_SIZE); elem_cnt = 0; - head_cnt = 0; + *head_cnt = 0; while (fillsize > 0 && elem_cnt < VIRTQUEUE_MAX_SIZE) { struct iovec *iov; size_t frame_size, dlen; @@ -221,7 +220,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, ASSERT(iov->iov_len >= hdrlen); iov->iov_base = (char *)iov->iov_base + hdrlen; iov->iov_len -= hdrlen; - head[head_cnt++] = elem_cnt; + head[(*head_cnt)++] = elem_cnt; fillsize -= dlen; elem_cnt += cnt; @@ -261,17 +260,18 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, len -= iov->iov_len; } /* adjust head count */ - while (head_cnt > 0 && head[head_cnt - 1] >= i) - head_cnt--; + while (*head_cnt > 0 && head[*head_cnt - 1] >= i) + (*head_cnt)--; + /* mark end of array */ - head[head_cnt] = i; + head[*head_cnt] = i; *iov_cnt = i; /* release unused buffers */ vu_queue_rewind(vq, elem_cnt - i); /* restore space for headers in iov */ - for (i = 0; i < head_cnt; i++) { + for (i = 0; i < *head_cnt; i++) { struct iovec *iov = &elem[head[i]].in_sg[0]; iov->iov_base = (char *)iov->iov_base - hdrlen; @@ -357,11 +357,11 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) struct vu_dev *vdev = c->vdev; struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE]; ssize_t len, previous_dlen; + int i, iov_cnt, head_cnt; size_t hdrlen, fillsize; int v6 = CONN_V6(conn); uint32_t already_sent; const uint16_t *check; - int i, iov_cnt; if (!vu_queue_enabled(vq) || !vu_queue_started(vq)) { debug("Got packet, but RX virtqueue not usable yet"); @@ -396,7 +396,8 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) /* collect the buffers from vhost-user and fill them with the * data from the socket */ - len = tcp_vu_sock_recv(c, conn, v6, already_sent, fillsize, &iov_cnt); + len = tcp_vu_sock_recv(c, conn, v6, already_sent, fillsize, + &iov_cnt, &head_cnt); if (len < 0) { if (len != -EAGAIN && len != -EWOULDBLOCK) { tcp_rst(c, conn);
On Tue, 18 Feb 2025 09:01:30 +0100 Laurent Vivier <lvivier(a)redhat.com> wrote:On 18/02/2025 03:50, David Gibson wrote:Well, it would still be in the data segment, not actually on the heap [1], but it would be somewhat hidden in the function. I'd rather suggest that we keep this stuff visible at the "top level". [1] I had a doubt for a moment so I tried it: $ git diff diff --git a/tcp_vu.c b/tcp_vu.c index 0622f17..c40b102 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -187,6 +187,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, { struct vu_dev *vdev = c->vdev; struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE]; + static char am_i_heap_or_am_i_data[64 << 20]; struct msghdr mh_sock = { 0 }; uint16_t mss = MSS_GET(conn); int s = conn->sock; @@ -195,6 +196,8 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, int elem_cnt; int i; + memset(am_i_heap_or_am_i_data, 0, sizeof(am_i_heap_or_am_i_data)); + *iov_cnt = 0; hdrlen = tcp_vu_hdrlen(v6); $ nm -td -S passt | grep am_i_heap_or_am_i_data 0000000202163552 0000000067108864 b am_i_heap_or_am_i_data.2 -- Stefanohead_cnt is a global variable which tracks how many entries in head[] are currently used. The fact that it's global obscures the fact that the lifetime over which it has a meaningful value is quite short: a single call to of tcp_vu_data_from_sock(). Make it a local to tcp_vu_data_from_sock() to make that lifetime clearer. We keep the head[] array global for now - although technically it has the same valid lifetime - because it's large enough we might not want to put it on the stack.We can make the array local but on the heap using a static declaration in the function.
On Tue, Feb 18, 2025 at 09:01:30AM +0100, Laurent Vivier wrote:On 18/02/2025 03:50, David Gibson wrote:We could. I kind of dislike static locals, as a rule, because it's pretty easy to miss them and make things non-reentrant by accident.head_cnt is a global variable which tracks how many entries in head[] are currently used. The fact that it's global obscures the fact that the lifetime over which it has a meaningful value is quite short: a single call to of tcp_vu_data_from_sock(). Make it a local to tcp_vu_data_from_sock() to make that lifetime clearer. We keep the head[] array global for now - although technically it has the same valid lifetime - because it's large enough we might not want to put it on the stack.We can make the array local but on the heap using a static declaration in the function.Reviewed-by: Laurent Vivier <lvivier(a)redhat.com>-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibsonCc: Laurent Vivier <lvivier(a)redhat.com> Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au> --- tcp_vu.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-) diff --git a/tcp_vu.c b/tcp_vu.c index 0622f173..6891ed13 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -38,7 +38,6 @@ static struct iovec iov_vu[VIRTQUEUE_MAX_SIZE + 1]; static struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE]; static int head[VIRTQUEUE_MAX_SIZE + 1]; -static int head_cnt; /** * tcp_vu_hdrlen() - return the size of the header in level 2 frame (TCP) @@ -183,7 +182,7 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) static ssize_t tcp_vu_sock_recv(const struct ctx *c, const struct tcp_tap_conn *conn, bool v6, uint32_t already_sent, size_t fillsize, - int *iov_cnt) + int *iov_cnt, int *head_cnt) { struct vu_dev *vdev = c->vdev; struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE]; @@ -202,7 +201,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, vu_init_elem(elem, &iov_vu[1], VIRTQUEUE_MAX_SIZE); elem_cnt = 0; - head_cnt = 0; + *head_cnt = 0; while (fillsize > 0 && elem_cnt < VIRTQUEUE_MAX_SIZE) { struct iovec *iov; size_t frame_size, dlen; @@ -221,7 +220,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, ASSERT(iov->iov_len >= hdrlen); iov->iov_base = (char *)iov->iov_base + hdrlen; iov->iov_len -= hdrlen; - head[head_cnt++] = elem_cnt; + head[(*head_cnt)++] = elem_cnt; fillsize -= dlen; elem_cnt += cnt; @@ -261,17 +260,18 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, len -= iov->iov_len; } /* adjust head count */ - while (head_cnt > 0 && head[head_cnt - 1] >= i) - head_cnt--; + while (*head_cnt > 0 && head[*head_cnt - 1] >= i) + (*head_cnt)--; + /* mark end of array */ - head[head_cnt] = i; + head[*head_cnt] = i; *iov_cnt = i; /* release unused buffers */ vu_queue_rewind(vq, elem_cnt - i); /* restore space for headers in iov */ - for (i = 0; i < head_cnt; i++) { + for (i = 0; i < *head_cnt; i++) { struct iovec *iov = &elem[head[i]].in_sg[0]; iov->iov_base = (char *)iov->iov_base - hdrlen; @@ -357,11 +357,11 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) struct vu_dev *vdev = c->vdev; struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE]; ssize_t len, previous_dlen; + int i, iov_cnt, head_cnt; size_t hdrlen, fillsize; int v6 = CONN_V6(conn); uint32_t already_sent; const uint16_t *check; - int i, iov_cnt; if (!vu_queue_enabled(vq) || !vu_queue_started(vq)) { debug("Got packet, but RX virtqueue not usable yet"); @@ -396,7 +396,8 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) /* collect the buffers from vhost-user and fill them with the * data from the socket */ - len = tcp_vu_sock_recv(c, conn, v6, already_sent, fillsize, &iov_cnt); + len = tcp_vu_sock_recv(c, conn, v6, already_sent, fillsize, + &iov_cnt, &head_cnt); if (len < 0) { if (len != -EAGAIN && len != -EWOULDBLOCK) { tcp_rst(c, conn);
On Tue, 18 Feb 2025 13:50:13 +1100 David Gibson <david(a)gibson.dropbear.id.au> wrote:head_cnt is a global variable which tracks how many entries in head[] are currently used. The fact that it's global obscures the fact that the lifetime over which it has a meaningful value is quite short: a single call to of tcp_vu_data_from_sock(). Make it a local to tcp_vu_data_from_sock() to make that lifetime clearer. We keep the head[] array global for now - although technically it has the same valid lifetime - because it's large enough we might not want to put it on the stack. Cc: Laurent Vivier <lvivier(a)redhat.com> Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>Applied. -- Stefano