net: skb: free up one bit in tx_flags

The linked series wants to add skb tx completion timestamps.
That needs a bit in skb_shared_info.tx_flags, but all are in use.

A per-skb bit is only needed for features that are configured on a
per packet basis. Per socket features can be read from sk->sk_tsflags.

Per packet tsflags can be set in sendmsg using cmsg, but only those in
SOF_TIMESTAMPING_TX_RECORD_MASK.

Per packet tsflags can also be set without cmsg by sandwiching a
send inbetween two setsockopts:

    val |= SOF_TIMESTAMPING_$FEATURE;
    setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &val, sizeof(val));
    write(fd, buf, sz);
    val &= ~SOF_TIMESTAMPING_$FEATURE;
    setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &val, sizeof(val));

Changing a datapath test from skb_shinfo(skb)->tx_flags to
skb->sk->sk_tsflags can change behavior in that case, as the tx_flags
is written before the second setsockopt updates sk_tsflags.

Therefore, only bits can be reclaimed that cannot be set by cmsg and
are also highly unlikely to be used to target individual packets
otherwise.

Free up the bit currently used for SKBTX_HW_TSTAMP_USE_CYCLES. This
selects between clock and free running counter source for HW TX
timestamps. It is probable that all packets of the same socket will
always use the same source.

Link: https://lore.kernel.org/netdev/cover.1739988644.git.pav@iki.fi/
Signed-off-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Reviewed-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Link: https://patch.msgid.link/20250225023416.2088705-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/engleder/tsnep_main.c b/drivers/net/ethernet/engleder/tsnep_main.c
index 0d030cb0b21c74446b86c903c67793a3c9292d29..3de4cb06e2668fbdd2c8623960a2034b881800ce 100644 (file)
--- a/drivers/net/ethernet/engleder/tsnep_main.c
+++ b/drivers/net/ethernet/engleder/tsnep_main.c
@@ -852,8 +852,8 @@ static bool tsnep_tx_poll(struct tsnep_tx *tx, int napi_budget)
                        struct skb_shared_hwtstamps hwtstamps;
                        u64 timestamp;
 
-                       if (skb_shinfo(entry->skb)->tx_flags &
-                           SKBTX_HW_TSTAMP_USE_CYCLES)
+                       if (entry->skb->sk &&
+                           READ_ONCE(entry->skb->sk->sk_tsflags) & SOF_TIMESTAMPING_BIND_PHC)
                                timestamp =
                                        __le64_to_cpu(entry->desc_wb->counter);
                        else

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 3044392e8ded8619434040b9ccaa6b1babdbf685..472f009630c98e60c7166ceb8d05cb094f6c837b 100644 (file)
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -1668,7 +1668,8 @@ done:
                if (igc_request_tx_tstamp(adapter, skb, &tstamp_flags)) {
                        skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
                        tx_flags |= IGC_TX_FLAGS_TSTAMP | tstamp_flags;
-                       if (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP_USE_CYCLES)
+                       if (skb->sk &&
+                           READ_ONCE(skb->sk->sk_tsflags) & SOF_TIMESTAMPING_BIND_PHC)
                                tx_flags |= IGC_TX_FLAGS_TSTAMP_TIMER_1;
                } else {
                        adapter->tx_hwtstamp_skipped++;

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f2bb8473d99a57e341366c6cbbd6a1e2d03881ca..171aa15f65414351f77ce170a332890240af1635 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -478,8 +478,8 @@ enum {
        /* device driver is going to provide hardware time stamp */
        SKBTX_IN_PROGRESS = 1 << 2,
 
-       /* generate hardware time stamp based on cycles if supported */
-       SKBTX_HW_TSTAMP_USE_CYCLES = 1 << 3,
+       /* reserved */
+       SKBTX_RESERVED = 1 << 3,
 
        /* generate wifi status information (where possible) */
        SKBTX_WIFI_STATUS = 1 << 4,
@@ -500,7 +500,6 @@ enum {
                                 SKBTX_SCHED_TSTAMP | \
                                 SKBTX_BPF)
 #define SKBTX_ANY_TSTAMP       (SKBTX_HW_TSTAMP | \
-                                SKBTX_HW_TSTAMP_USE_CYCLES | \
                                 SKBTX_ANY_SW_TSTAMP)
 
 /* Definitions for flags in struct skb_shared_info */

diff --git a/net/socket.c b/net/socket.c
index 0545e9ea705815678f436cd26aaf229308ed3a1f..b64ecf2722e7b8df2e724780acb78a4a3f0cc244 100644 (file)
--- a/net/socket.c
+++ b/net/socket.c
@@ -680,18 +680,9 @@ void __sock_tx_timestamp(__u32 tsflags, __u8 *tx_flags)
 {
        u8 flags = *tx_flags;
 
-       if (tsflags & SOF_TIMESTAMPING_TX_HARDWARE) {
+       if (tsflags & SOF_TIMESTAMPING_TX_HARDWARE)
                flags |= SKBTX_HW_TSTAMP_NOBPF;
 
-               /* PTP hardware clocks can provide a free running cycle counter
-                * as a time base for virtual clocks. Tell driver to use the
-                * free running cycle counter for timestamp if socket is bound
-                * to virtual clock.
-                */
-               if (tsflags & SOF_TIMESTAMPING_BIND_PHC)
-                       flags |= SKBTX_HW_TSTAMP_USE_CYCLES;
-       }
-
        if (tsflags & SOF_TIMESTAMPING_TX_SOFTWARE)
                flags |= SKBTX_SW_TSTAMP;