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Expand comments relating various detach/free/drop inpcb routines.

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MFC after:	3 days
This commit is contained in:
Robert Watson 2008-09-29 13:50:17 +00:00
parent fc18af966f
commit c0a211c51f
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=183461
1 changed files with 31 additions and 9 deletions
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40
sys/netinet/in_pcb.c
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@ -684,21 +684,29 @@ in_pcbdisconnect(struct inpcb *inp)
}
/*
* In the old world order, in_pcbdetach() served two functions: to detach the
* pcb from the socket/potentially free the socket, and to free the pcb
* itself. In the new world order, the protocol code is responsible for
* managing the relationship with the socket, and this code simply frees the
* pcb.
* Historically, in_pcbdetach() included the functionality now found in
* in_pcbfree() and in_pcbdrop(). They are now broken out to reflect the
* more complex life cycle of TCP.
*
* in_pcbdetach() is responsibe for disconnecting the socket from an inpcb.
* For most protocols, this will be invoked immediately prior to calling
* in_pcbfree(). However, for TCP the inpcb may significantly outlive the
* socket, in which case in_pcbfree() may be deferred.
*/
void
in_pcbdetach(struct inpcb *inp)
{
KASSERT(inp->inp_socket != NULL, ("in_pcbdetach: inp_socket == NULL"));
inp->inp_socket->so_pcb = NULL;
inp->inp_socket = NULL;
}
/*
* in_pcbfree() is responsible for freeing an already-detached inpcb, as well
* as removing it from any global inpcb lists it might be on.
*/
void
in_pcbfree(struct inpcb *inp)
{
@ -728,10 +736,24 @@ in_pcbfree(struct inpcb *inp)
}
/*
* TCP needs to maintain its inpcb structure after the TCP connection has
* been torn down. However, it must be disconnected from the inpcb hashes as
* it must not prevent binding of future connections to the same port/ip
* combination by other inpcbs.
* in_pcbdrop() removes an inpcb from hashed lists, releasing its address and
* port reservation, and preventing it from being returned by inpcb lookups.
*
* It is used by TCP to mark an inpcb as unused and avoid future packet
* delivery or event notification when a socket remains open but TCP has
* closed. This might occur as a result of a shutdown()-initiated TCP close
* or a RST on the wire, and allows the port binding to be reused while still
* maintaining the invariant that so_pcb always points to a valid inpcb until
* in_pcbdetach().
*
* XXXRW: An inp_lport of 0 is used to indicate that the inpcb is not on hash
* lists, but can lead to confusing netstat output, as open sockets with
* closed TCP connections will no longer appear to have their bound port
* number. An explicit flag would be better, as it would allow us to leave
* the port number intact after the connection is dropped.
*
* XXXRW: Possibly in_pcbdrop() should also prevent future notifications by
* in_pcbnotifyall() and in_pcbpurgeif0()?
*/
void
in_pcbdrop(struct inpcb *inp)