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Message-ID: <E216E06A-0BE4-4221-BBF6-03017AB7D720@gmail.com>
Date: Wed, 23 Oct 2019 17:10:33 -0700
From: "Jonathan Lemon" <jonathan.lemon@...il.com>
To: "Magnus Karlsson" <magnus.karlsson@...el.com>
Cc: bjorn.topel@...el.com, ast@...nel.org, daniel@...earbox.net,
netdev@...r.kernel.org, bpf@...r.kernel.org, degeneloy@...il.com,
john.fastabend@...il.com
Subject: Re: [PATCH bpf-next v2] libbpf: fix compatibility for kernels without
need_wakeup
On 22 Oct 2019, at 1:25, Magnus Karlsson wrote:
> When the need_wakeup flag was added to AF_XDP, the format of the
> XDP_MMAP_OFFSETS getsockopt was extended. Code was added to the
> kernel to take care of compatibility issues arrising from running
> applications using any of the two formats. However, libbpf was
> not extended to take care of the case when the application/libbpf
> uses the new format but the kernel only supports the old
> format. This patch adds support in libbpf for parsing the old
> format, before the need_wakeup flag was added, and emulating a
> set of static need_wakeup flags that will always work for the
> application.
>
> v1 -> v2:
> * Rebased to bpf-next
> * Rewrote the code as the previous version made you blind
>
> Fixes: a4500432c2587cb2a ("libbpf: add support for need_wakeup flag in
> AF_XDP part")
> Reported-by: Eloy Degen <degeneloy@...il.com>
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> ---
> tools/lib/bpf/xsk.c | 79
> +++++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 67 insertions(+), 12 deletions(-)
>
> diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> index 7866500..aa16458 100644
> --- a/tools/lib/bpf/xsk.c
> +++ b/tools/lib/bpf/xsk.c
> @@ -73,6 +73,21 @@ struct xsk_nl_info {
> int fd;
> };
>
> +/* Up until and including Linux 5.3 */
> +struct xdp_ring_offset_no_flags {
> + __u64 producer;
> + __u64 consumer;
> + __u64 desc;
> +};
> +
> +/* Up until and including Linux 5.3 */
> +struct xdp_mmap_offsets_no_flags {
> + struct xdp_ring_offset_no_flags rx;
> + struct xdp_ring_offset_no_flags tx;
> + struct xdp_ring_offset_no_flags fr;
> + struct xdp_ring_offset_no_flags cr;
> +};
Why not name these with "_v1" instead of "_no_flags" in order to match
the same definitions in net/xdp/xsk.h? I'd rather not have two
identical
structures different names if it can be avoided.
> +
> int xsk_umem__fd(const struct xsk_umem *umem)
> {
> return umem ? umem->fd : -EINVAL;
> @@ -133,6 +148,54 @@ static int xsk_set_xdp_socket_config(struct
> xsk_socket_config *cfg,
> return 0;
> }
>
> +static bool xsk_mmap_offsets_has_flags(socklen_t optlen)
> +{
> + return (optlen == sizeof(struct xdp_mmap_offsets)) ? true : false;
> +}
> +
> +static int xsk_get_mmap_offsets(int fd, struct xdp_mmap_offsets *off)
> +{
> + struct xdp_mmap_offsets_no_flags off_no_flag;
> + socklen_t optlen;
> + int err;
> +
> + optlen = sizeof(*off);
> + err = getsockopt(fd, SOL_XDP, XDP_MMAP_OFFSETS, off, &optlen);
> + if (err)
> + return err;
> +
> + if (xsk_mmap_offsets_has_flags(optlen))
I'd just use "if (optlen == sizeof(*off))" here.
> + return 0;
> +
> + /* getsockopt on a kernel <= 5.3 has no flags fields.
> + * Copy over the offsets to the correct places in the >=5.4 format
> + * and put the flags where they would have been on that kernel.
> + */
Would it be worthwhile adding a length check here?
Something like:
if (optlen == sizeof(struct xdp_mmap_offsets_v1)
return xsk_mmap_offset_v1(off);
return -EINVAL;
Which makes it easy to revisit this later if the same
problem crops up again.
> + memcpy(&off_no_flag, off, sizeof(off_no_flag));
> +
> + off->rx.producer = off_no_flag.rx.producer;
> + off->rx.consumer = off_no_flag.rx.consumer;
> + off->rx.desc = off_no_flag.rx.desc;
> + off->rx.flags = off_no_flag.rx.consumer + sizeof(u32);
> +
> + off->tx.producer = off_no_flag.tx.producer;
> + off->tx.consumer = off_no_flag.tx.consumer;
> + off->tx.desc = off_no_flag.tx.desc;
> + off->tx.flags = off_no_flag.tx.consumer + sizeof(u32);
> +
> + off->fr.producer = off_no_flag.fr.producer;
> + off->fr.consumer = off_no_flag.fr.consumer;
> + off->fr.desc = off_no_flag.fr.desc;
> + off->fr.flags = off_no_flag.fr.consumer + sizeof(u32);
> +
> + off->cr.producer = off_no_flag.cr.producer;
> + off->cr.consumer = off_no_flag.cr.consumer;
> + off->cr.desc = off_no_flag.cr.desc;
> + off->cr.flags = off_no_flag.cr.consumer + sizeof(u32);
Then all this moves into a xsk_mmap_offset_v1() helper.
--
Jonathan
> +
> + return 0;
> +}
> +
> int xsk_umem__create_v0_0_4(struct xsk_umem **umem_ptr, void
> *umem_area,
> __u64 size, struct xsk_ring_prod *fill,
> struct xsk_ring_cons *comp,
> @@ -141,7 +204,6 @@ int xsk_umem__create_v0_0_4(struct xsk_umem
> **umem_ptr, void *umem_area,
> struct xdp_mmap_offsets off;
> struct xdp_umem_reg mr;
> struct xsk_umem *umem;
> - socklen_t optlen;
> void *map;
> int err;
>
> @@ -190,8 +252,7 @@ int xsk_umem__create_v0_0_4(struct xsk_umem
> **umem_ptr, void *umem_area,
> goto out_socket;
> }
>
> - optlen = sizeof(off);
> - err = getsockopt(umem->fd, SOL_XDP, XDP_MMAP_OFFSETS, &off,
> &optlen);
> + err = xsk_get_mmap_offsets(umem->fd, &off);
> if (err) {
> err = -errno;
> goto out_socket;
> @@ -492,7 +553,6 @@ int xsk_socket__create(struct xsk_socket
> **xsk_ptr, const char *ifname,
> struct sockaddr_xdp sxdp = {};
> struct xdp_mmap_offsets off;
> struct xsk_socket *xsk;
> - socklen_t optlen;
> int err;
>
> if (!umem || !xsk_ptr || !rx || !tx)
> @@ -551,8 +611,7 @@ int xsk_socket__create(struct xsk_socket
> **xsk_ptr, const char *ifname,
> }
> }
>
> - optlen = sizeof(off);
> - err = getsockopt(xsk->fd, SOL_XDP, XDP_MMAP_OFFSETS, &off, &optlen);
> + err = xsk_get_mmap_offsets(xsk->fd, &off);
> if (err) {
> err = -errno;
> goto out_socket;
> @@ -638,7 +697,6 @@ int xsk_socket__create(struct xsk_socket
> **xsk_ptr, const char *ifname,
> int xsk_umem__delete(struct xsk_umem *umem)
> {
> struct xdp_mmap_offsets off;
> - socklen_t optlen;
> int err;
>
> if (!umem)
> @@ -647,8 +705,7 @@ int xsk_umem__delete(struct xsk_umem *umem)
> if (umem->refcount)
> return -EBUSY;
>
> - optlen = sizeof(off);
> - err = getsockopt(umem->fd, SOL_XDP, XDP_MMAP_OFFSETS, &off,
> &optlen);
> + err = xsk_get_mmap_offsets(umem->fd, &off);
> if (!err) {
> munmap(umem->fill->ring - off.fr.desc,
> off.fr.desc + umem->config.fill_size * sizeof(__u64));
> @@ -666,7 +723,6 @@ void xsk_socket__delete(struct xsk_socket *xsk)
> {
> size_t desc_sz = sizeof(struct xdp_desc);
> struct xdp_mmap_offsets off;
> - socklen_t optlen;
> int err;
>
> if (!xsk)
> @@ -677,8 +733,7 @@ void xsk_socket__delete(struct xsk_socket *xsk)
> close(xsk->prog_fd);
> }
>
> - optlen = sizeof(off);
> - err = getsockopt(xsk->fd, SOL_XDP, XDP_MMAP_OFFSETS, &off, &optlen);
> + err = xsk_get_mmap_offsets(xsk->fd, &off);
> if (!err) {
> if (xsk->rx) {
> munmap(xsk->rx->ring - off.rx.desc,
> --
> 2.7.4
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