Re: [PATCH] netlink: NL_SET_ERR_MSG - remove local static array
From: Joe Perches
Date: Wed Aug 11 2021 - 00:07:18 EST
On Tue, 2021-08-10 at 13:30 -0700, Jakub Kicinski wrote:
> On Mon, 09 Aug 2021 10:04:00 -0700 Joe Perches wrote:
> > The want was to have some separate object section for netlink messages
> > so all netlink messages could be specifically listed by some tool but
> > the effect is duplicating static const char arrays in the object code.
> >
> > It seems unused presently so change the macro to avoid the local static
> > declarations until such time as these actually are wanted and used.
> >
> > This reduces object size ~8KB in an x86-64 defconfig without modules.
[]
> > diff --git a/include/linux/netlink.h b/include/linux/netlink.h
[]
> > @@ -89,13 +89,12 @@ struct netlink_ext_ack {
> > * to the lack of an output buffer.)
> > */
> > #define NL_SET_ERR_MSG(extack, msg) do { \
> > - static const char __msg[] = msg; \
> > struct netlink_ext_ack *__extack = (extack); \
> > \
> > - do_trace_netlink_extack(__msg); \
> > + do_trace_netlink_extack(msg); \
> > \
> > if (__extack) \
> > - __extack->_msg = __msg; \
> > + __extack->_msg = msg; \
> > } while (0)
>
> But you've made us evaluate msg multiple times now.
> Given extack is carefully evaluated only once this stands out.
msg is always a const char array so no evaluation is done.
It's just a pointer.
In fact, this could either become a static inline or a
simple function call to reduce object size even further.
For instance:
$ size vmlinux.o.nl_func.*
text data bss dec hex filename
19974564 3457991 741312 24173867 170dd2b vmlinux.o.nl_func.new
19992097 3457967 741312 24191376 1712190 vmlinux.o.nl_func.old
---
include/linux/netlink.h | 29 ++++++++++-------------------
net/netlink/af_netlink.c | 13 +++++++++++++
2 files changed, 23 insertions(+), 19 deletions(-)
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 61b1c7fcc401e..fe80c2704cc23 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -82,21 +82,16 @@ struct netlink_ext_ack {
u8 cookie_len;
};
+void netlink_set_err_msg(struct netlink_ext_ack *extack, const char *msg);
/* Always use this macro, this allows later putting the
* message into a separate section or such for things
* like translation or listing all possible messages.
* Currently string formatting is not supported (due
* to the lack of an output buffer.)
*/
-#define NL_SET_ERR_MSG(extack, msg) do { \
- static const char __msg[] = msg; \
- struct netlink_ext_ack *__extack = (extack); \
- \
- do_trace_netlink_extack(__msg); \
- \
- if (__extack) \
- __extack->_msg = __msg; \
-} while (0)
+
+#define NL_SET_ERR_MSG(extack, msg) \
+ netlink_set_err_msg(extack, msg)
#define NL_SET_ERR_MSG_MOD(extack, msg) \
NL_SET_ERR_MSG((extack), KBUILD_MODNAME ": " msg)
@@ -110,16 +105,12 @@ struct netlink_ext_ack {
#define NL_SET_BAD_ATTR(extack, attr) NL_SET_BAD_ATTR_POLICY(extack, attr, NULL)
-#define NL_SET_ERR_MSG_ATTR_POL(extack, attr, pol, msg) do { \
- static const char __msg[] = msg; \
- struct netlink_ext_ack *__extack = (extack); \
- \
- do_trace_netlink_extack(__msg); \
- \
- if (__extack) { \
- __extack->_msg = __msg; \
- __extack->bad_attr = (attr); \
- __extack->policy = (pol); \
+#define NL_SET_ERR_MSG_ATTR_POL(extack, attr, pol, msg) \
+do { \
+ netlink_set_err_msg(extack, msg); \
+ if (extack) { \
+ extack->bad_attr = (attr); \
+ extack->policy = (pol); \
} \
} while (0)
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 24b7cf447bc55..b6d035f0d343b 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2561,6 +2561,19 @@ int nlmsg_notify(struct sock *sk, struct sk_buff *skb, u32 portid,
}
EXPORT_SYMBOL(nlmsg_notify);
+/**
+ * nl_set_err_msg -
+ */
+
+void netlink_set_err_msg(struct netlink_ext_ack *extack, const char *msg)
+{
+ do_trace_netlink_extack(msg);
+
+ if (extack)
+ extack->_msg = msg;
+}
+EXPORT_SYMBOL(netlink_set_err_msg);
+
#ifdef CONFIG_PROC_FS
struct nl_seq_iter {
struct seq_net_private p;