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Commit 36154388 authored by Alessandro Rubini's avatar Alessandro Rubini
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doc: documented stamp in 2.6.39

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doc/wrs-test.in
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......@@ -180,8 +180,8 @@ Rabbit.
The hardware timestamping mechanism has been pushed to the upstream
kernel by Patrick Ohly and Richard Cochran; the first official kernel
released with some related code was 2.6.30.
The description in this section refers to Linux-2.6.35, although I
plan to update to later versions over time.
The description in this section refers to Linux-2.6.39, with references
to the slightly-different implementation of 2.6.35.
@c v2.6.35-rc1-1246-gc1f19b5
The official documentation can be found in
......@@ -365,13 +365,14 @@ The flow of actions that are involved in stamping is as follows:
@item In the @i{start_xmit} device function, the driver marks timestamping
as @i{in_progress} in the socket buffer -- only if this packet is going
to be stamped.
to be stamped. This is accomplished by setting the @code{SKBTX_IN_PROGRESS}
bit in @code{skb_shinfo(skb)->tx_flags}.
@item For those packets where @i{in_progress} is set, the @i{tx-done} interrupt function retrieves the timestamp and
calls @i{skb_tstamp_tx} (@code{net/core/skbuff.c}). Note that the
@i{in_progress} marker is only used by the driver itself.
@code{SKBTX_IN_PROGRESS} flag is only used by the driver itself.
@item This @i{skb_stamp_tx} copies over the data to a clone of the
@item This @i{skb_tstamp_tx} copies over the data to a clone of the
original socket buffer, which is then enqueued to the error queue
for the socket. The @i{tx-done} code can thus release this @i{skb}
without any further special case.
......@@ -399,9 +400,15 @@ for those packets where @i{in_progress} was set:
skb_tstamp_tx(skb, &shhwtstamps);
@end smallexample
Actually, the only difference in the code is that the structure
Actually, the only difference in the transmit code path from the
receive code path we have seen earlier is that the structure
with the two @i{ktime} stamps is local and not in the @i{skb} itself.
Before version @code{v2.6.36-rc1-71-g2244d07} (thus, in 2.6.35 and earlier)
the @i{in_progress} marker was a field in a union hosted in the
socket buffer, but this extra level of indirection was confusing and has
been removed.
@c ==========================================================================
@node Timestamping Use
@section Timestamping Use
......
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