| Message ID | 20250529001315.233492-5-changwoo@igalia.com |
|---|---|
| State | New |
| Headers | show |
| Series | [01/11] PM: EM: Add ENERGY_MODEL_NETLINK Kconfig. | expand |
On Thu, May 29, 2025 at 09:13:08AM +0900, Changwoo Min wrote: > +static int em_genl_cmd_doit(struct sk_buff *skb, struct genl_info *info) > +{ > + struct param p = { .attrs = info->attrs }; > + struct sk_buff *msg; > + void *hdr; > + int cmd = info->genlhdr->cmd; > + int ret = -EMSGSIZE; > + > + msg = genlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL); > + if (!msg) > + return -ENOMEM; Just a heads-up, I know everyone recommends NLMSG_GOODSIZE but in reality it's not that great because netlink_trim() reallocates the skb and copies the entire linear buffer if it determines that the skb is half-empty. Performance suffers as a result. So it's actually better to calculate the exact message length prior to allocation. See the SPDM commit referenced in my previous e-mail. Another lesson I had to learn the hard way. :( Thanks, Lukas
On 6/2/25 04:59, Lukas Wunner wrote: > On Thu, May 29, 2025 at 09:13:08AM +0900, Changwoo Min wrote: >> +static int em_genl_cmd_doit(struct sk_buff *skb, struct genl_info *info) >> +{ >> + struct param p = { .attrs = info->attrs }; >> + struct sk_buff *msg; >> + void *hdr; >> + int cmd = info->genlhdr->cmd; >> + int ret = -EMSGSIZE; >> + >> + msg = genlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL); >> + if (!msg) >> + return -ENOMEM; > > Just a heads-up, I know everyone recommends NLMSG_GOODSIZE but in reality > it's not that great because netlink_trim() reallocates the skb and copies > the entire linear buffer if it determines that the skb is half-empty. > Performance suffers as a result. So it's actually better to calculate > the exact message length prior to allocation. Thank you, Lukas, for sharing the experience. I will address it in the next version. Regards, Changwoo Min
diff --git a/kernel/power/em_netlink.c b/kernel/power/em_netlink.c index 30d83fb5a3a8..edbaecebd0b4 100644 --- a/kernel/power/em_netlink.c +++ b/kernel/power/em_netlink.c @@ -23,14 +23,65 @@ static const struct genl_multicast_group em_genl_mcgrps[] = { static const struct nla_policy em_genl_policy[EM_GENL_ATTR_MAX + 1] = { }; +struct param { + struct nlattr **attrs; + struct sk_buff *msg; +}; + +typedef int (*cb_t)(struct param *); + static struct genl_family em_genl_family; +/*************************** Command encoding ********************************/ -static int em_genl_cmd_doit(struct sk_buff *skb, struct genl_info *info) +static int em_genl_cmd_pd_get_id(struct param *p) { return -ENOTSUPP; } +static int em_genl_cmd_pd_get_tbl(struct param *p) +{ + return -ENOTSUPP; +} + +static const cb_t cmd_cb[] = { + [EM_GENL_CMD_PD_GET_ID] = em_genl_cmd_pd_get_id, + [EM_GENL_CMD_PD_GET_TBL] = em_genl_cmd_pd_get_tbl, +}; + +static int em_genl_cmd_doit(struct sk_buff *skb, struct genl_info *info) +{ + struct param p = { .attrs = info->attrs }; + struct sk_buff *msg; + void *hdr; + int cmd = info->genlhdr->cmd; + int ret = -EMSGSIZE; + + msg = genlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL); + if (!msg) + return -ENOMEM; + p.msg = msg; + + hdr = genlmsg_put_reply(msg, info, &em_genl_family, 0, cmd); + if (!hdr) + goto out_free_msg; + + ret = cmd_cb[cmd](&p); + if (ret) + goto out_cancel_msg; + + genlmsg_end(msg, hdr); + + return genlmsg_reply(msg, info); + +out_cancel_msg: + genlmsg_cancel(msg, hdr); +out_free_msg: + nlmsg_free(msg); + + return ret; +} + static const struct genl_small_ops em_genl_ops[] = { { .cmd = EM_GENL_CMD_PD_GET_ID,
The infrastructure for command processing receives a command from a userspace and calls a callback corresponding to the request command. Note that the callback functions are just boilerplates in this commit, and the actual implementations will be provided in the following commits when a callback for a specific command is implemented. Signed-off-by: Changwoo Min <changwoo@igalia.com> --- kernel/power/em_netlink.c | 53 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 52 insertions(+), 1 deletion(-)