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libnl: recvmsgs doesn't necessarily free the message data

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I stepped over libnl always freeing the messages and it
kind of made it awkward to reuse the message data without
reallocating.

The basic idea is: if a callback return value has a bit set,
don't free that message. The calling application owns it.
By default, things stay as before (messages are freed).

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
This commit is contained in:
Inaky Perez-Gonzalez 2008-04-28 15:35:26 -07:00 • committed by Thomas Graf
parent 535e831622
commit 32000e8e9c
2 changed files with 36 additions and 3 deletions
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14
include/netlink/handlers.h
View file

@ -64,6 +64,20 @@ enum nl_cb_action {
NL_STOP,
};
/**
* Callback action modifiers
* @ingroup cb
*
* These should be ORed to the callback actions defined by enum
* nl_cb_action.
*/
enum nl_cb_action_mods {
/** Callee keeps the message, don't free */
NL_KEEP_MSG = 0x1000,
#define NL_KEEP_MSG NL_KEEP_MSG /* for config testing */
};
/* backwards compatibility */
#define NL_PROCEED NL_OK
#define NL_EXIT NL_STOP

25
lib/nl.c
View file

@ -551,6 +551,9 @@ abort:
#define NL_CB_CALL(cb, type, msg) \
do { \
err = nl_cb_call(cb, type, msg); \
if (free_msg && (err & NL_KEEP_MSG)) \
free_msg = 0; \
err &= ~NL_KEEP_MSG; \
switch (err) { \
case NL_OK: \
err = 0; \
@ -564,10 +567,23 @@ do { \
} \
} while (0)
/*
* NOTE: on handling freeing of the message data
*
* By default, the message data is freed after handling is done. In
* order to allow a callback using it after exiting the message
* handling loop, it can return NL_KEEP_MSG ORed to it's return code.
*
* Once the freeing of the message is disabled, it cannot be activated
* again; this way, if a callback decides to switch it off because it
* will keep the allocated data, another one cannot activate it, have
* it freed and cause a race condition with later access to that (now
* freed) data.
*/
static int recvmsgs(struct nl_handle *handle, struct nl_cb *cb)
{
int n, err = 0, multipart = 0;
unsigned char *buf = NULL;
unsigned char *buf = NULL, free_msg = 1;
struct nlmsghdr *hdr;
struct sockaddr_nl nla = {0};
struct nl_msg *msg = NULL;
@ -590,7 +606,9 @@ continue_reading:
NL_DBG(3, "recgmsgs(%p): Processing valid message...\n",
handle);
nlmsg_free(msg);
if (free_msg)
nlmsg_free(msg);
free_msg = 1; /* By default, we free the message data */
msg = nlmsg_convert(hdr);
if (!msg) {
err = nl_errno(ENOMEM);
@ -728,7 +746,8 @@ skip:
hdr = nlmsg_next(hdr, &n);
}
nlmsg_free(msg);
if (free_msg)
nlmsg_free(msg);
free(buf);
free(creds);
buf = NULL;