On 2/15/25 2:23 PM, Jason Xing wrote:
On Sun, Feb 16, 2025 at 2:08 AM Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
Jason Xing wrote:
On Sat, Feb 15, 2025 at 11:06 PM Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
Jason Xing wrote:
Support hw SCM_TSTAMP_SND case for bpf timestamping.
Add a new sock_ops callback, BPF_SOCK_OPS_TS_HW_OPT_CB. This
callback will occur at the same timestamping point as the user
space's hardware SCM_TSTAMP_SND. The BPF program can use it to
get the same SCM_TSTAMP_SND timestamp without modifying the
user-space application.
To avoid increasing the code complexity, replace SKBTX_HW_TSTAMP
with SKBTX_HW_TSTAMP_NOBPF instead of changing numerous callers
from driver side using SKBTX_HW_TSTAMP. The new definition of
SKBTX_HW_TSTAMP means the combination tests of socket timestamping
and bpf timestamping. After this patch, drivers can work under the
bpf timestamping.
Considering some drivers doesn't assign the skb with hardware
timestamp,
This is not for a real technical limitation, like the skb perhaps
being cloned or shared?
Agreed on this point. I'm kind of familiar with I40E, so I dare to say
the reason why it doesn't assign the hwtstamp is because the skb will
soon be destroyed, that is to say, it's pointless to assign the
timestamp.
Makes sense.
But that does not ensure that the skb is exclusively owned. Nor that
the same is true for all drivers using this API (which is not small,
but small enough to manually review if need be).
The first two examples I happened to look at, i40e and bnx2x, both use
skb_get() to get a non-exclusive skb reference for their ptp_tx_skb.
I think the existing __skb_tstamp_tx() function is also assigning to
skb_hwtstamps(skb). The skb may be cloned from the orig_skb first, but they
still share the same shinfo. My understanding is that this patch is assigning to
the shinfo earlier, so it should not have changed the driver's expectation on
the skb_hwtstamps(skb) after calling __skb_tstamp_tx(). If there are drivers
assuming exclusive access to the skb_hwtstamps(skb), probably it is something
that needs to be addressed regardless and should not be the common case?
