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netlink: add support for formatted extack messages

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Include an 80-byte buffer in struct netlink_ext_ack that can be used
 for scnprintf()ed messages.  This does mean that the resulting string
 can't be enumerated, translated etc. in the way NL_SET_ERR_MSG() was
 designed to allow.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Edward Cree 2022-10-18 15:37:27 +01:00 • committed by Jakub Kicinski
parent a526a3cc9c
commit 51c352bdbc
1 changed files with 27 additions and 2 deletions
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29
include/linux/netlink.h
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@ -64,6 +64,7 @@ netlink_kernel_create(struct net *net, int unit, struct netlink_kernel_cfg *cfg)
/* this can be increased when necessary - don't expose to userland */ /* this can be increased when necessary - don't expose to userland */
#define NETLINK_MAX_COOKIE_LEN 20 #define NETLINK_MAX_COOKIE_LEN 20
#define NETLINK_MAX_FMTMSG_LEN 80
/** /**
* struct netlink_ext_ack - netlink extended ACK report struct * struct netlink_ext_ack - netlink extended ACK report struct
@ -75,6 +76,8 @@ netlink_kernel_create(struct net *net, int unit, struct netlink_kernel_cfg *cfg)
* @miss_nest: nest missing an attribute (%NULL if missing top level attr) * @miss_nest: nest missing an attribute (%NULL if missing top level attr)
* @cookie: cookie data to return to userspace (for success) * @cookie: cookie data to return to userspace (for success)
* @cookie_len: actual cookie data length * @cookie_len: actual cookie data length
* @_msg_buf: output buffer for formatted message strings - don't access
* directly, use %NL_SET_ERR_MSG_FMT
*/ */
struct netlink_ext_ack { struct netlink_ext_ack {
const char *_msg; const char *_msg;
@ -84,13 +87,13 @@ struct netlink_ext_ack {
u16 miss_type; u16 miss_type;
u8 cookie[NETLINK_MAX_COOKIE_LEN]; u8 cookie[NETLINK_MAX_COOKIE_LEN];
u8 cookie_len; u8 cookie_len;
char _msg_buf[NETLINK_MAX_FMTMSG_LEN];
}; };
/* Always use this macro, this allows later putting the /* Always use this macro, this allows later putting the
* message into a separate section or such for things * message into a separate section or such for things
* like translation or listing all possible messages. * like translation or listing all possible messages.
* Currently string formatting is not supported (due * If string formatting is needed use NL_SET_ERR_MSG_FMT.
* to the lack of an output buffer.)
*/ */
#define NL_SET_ERR_MSG(extack, msg) do { \ #define NL_SET_ERR_MSG(extack, msg) do { \
static const char __msg[] = msg; \ static const char __msg[] = msg; \
@ -102,9 +105,31 @@ struct netlink_ext_ack {
__extack->_msg = __msg; \ __extack->_msg = __msg; \
} while (0) } while (0)
/* We splice fmt with %s at each end even in the snprintf so that both calls
* can use the same string constant, avoiding its duplication in .ro
*/
#define NL_SET_ERR_MSG_FMT(extack, fmt, args...) do { \
struct netlink_ext_ack *__extack = (extack); \
\
if (!__extack) \
break; \
if (snprintf(__extack->_msg_buf, NETLINK_MAX_FMTMSG_LEN, \
"%s" fmt "%s", "", ##args, "") >= \
NETLINK_MAX_FMTMSG_LEN) \
net_warn_ratelimited("%s" fmt "%s", "truncated extack: ", \
##args, "\n"); \
\
do_trace_netlink_extack(__extack->_msg_buf); \
\
__extack->_msg = __extack->_msg_buf; \
} while (0)
#define NL_SET_ERR_MSG_MOD(extack, msg) \ #define NL_SET_ERR_MSG_MOD(extack, msg) \
NL_SET_ERR_MSG((extack), KBUILD_MODNAME ": " msg) NL_SET_ERR_MSG((extack), KBUILD_MODNAME ": " msg)
#define NL_SET_ERR_MSG_FMT_MOD(extack, fmt, args...) \
NL_SET_ERR_MSG_FMT((extack), KBUILD_MODNAME ": " fmt, ##args)
#define NL_SET_BAD_ATTR_POLICY(extack, attr, pol) do { \ #define NL_SET_BAD_ATTR_POLICY(extack, attr, pol) do { \
if ((extack)) { \ if ((extack)) { \
(extack)->bad_attr = (attr); \ (extack)->bad_attr = (attr); \