[dm-devel] [PATCH 30/35] multipathd: uxlsnr: merge uxsock_trigger() into state machine
Benjamin Marzinski
bmarzins at redhat.com
Thu Sep 16 03:32:37 UTC 2021
On Fri, Sep 10, 2021 at 01:41:15PM +0200, mwilck at suse.com wrote:
> From: Martin Wilck <mwilck at suse.com>
>
> This patch sets up the bulk of the state machine. The idea is to
> fall through the case labels as long as possible (when steps succeed)
> and return to the caller if either an error occurs, or it becomes
> necessary to wait for some pollable condition.
>
> While doing this, switch to negative error codes for the functions
> in uxlsnr.c (e.g. parse_cmd()). Positive return codes are reserved
> for the cli_handler functions themselves. This way we can clearly
> distinguish the error source, and avoid confusion and misleading
> error messages. No cli_handler returns negative values.
>
> Note: with this patch applied, clients may hang and time out if
> the handler fails to acquire the vecs lock. This will be fixed in the
> follow-up patch "multipathd: uxlsnr: add idle notification".
>
> Signed-off-by: Martin Wilck <mwilck at suse.com>
> ---
> multipathd/uxlsnr.c | 145 ++++++++++++++++++++++++--------------------
> 1 file changed, 80 insertions(+), 65 deletions(-)
>
> diff --git a/multipathd/uxlsnr.c b/multipathd/uxlsnr.c
> index ff9604f..553274b 100644
> --- a/multipathd/uxlsnr.c
> +++ b/multipathd/uxlsnr.c
> @@ -299,22 +299,13 @@ static int parse_cmd(struct client *c)
>
> r = get_cmdvec(c->cmd, &c->cmdvec);
>
> - if (r) {
> - genhelp_handler(c->cmd, r, &c->reply);
> - if (get_strbuf_len(&c->reply) == 0)
> - return EINVAL;
> - return 0;
> - }
> + if (r)
> + return -r;
>
> c->handler = find_handler_for_cmdvec(c->cmdvec);
>
> - if (!c->handler || !c->handler->fn) {
> - genhelp_handler(c->cmd, EINVAL, &c->reply);
> - if (get_strbuf_len(&c->reply) == 0)
> - r = EINVAL;
> - else
> - r = 0;
> - }
> + if (!c->handler || !c->handler->fn)
> + return -EINVAL;
>
> return r;
> }
> @@ -325,7 +316,7 @@ static int execute_handler(struct client *c, struct vectors *vecs, int timeout)
> struct timespec tmo;
>
> if (!c->handler)
> - return EINVAL;
> + return -EINVAL;
>
> if (clock_gettime(CLOCK_REALTIME, &tmo) == 0) {
> tmo.tv_sec += timeout;
> @@ -355,50 +346,29 @@ static int execute_handler(struct client *c, struct vectors *vecs, int timeout)
> return r;
> }
>
> -static int uxsock_trigger(struct client *c, void *trigger_data)
> +void default_reply(struct client *c, int r)
> {
> - struct vectors * vecs;
> - int r = 1;
> -
> - vecs = (struct vectors *)trigger_data;
> -
> - r = parse_cmd(c);
> -
> - if (r == 0 && c->cmdvec && VECTOR_SIZE(c->cmdvec) > 0) {
> - struct key *kw = VECTOR_SLOT(c->cmdvec, 0);
> -
> - if (!c->is_root && kw->code != LIST)
> - r = EPERM;
> - }
> -
> - if (r == 0 && c->handler)
> - r = execute_handler(c, vecs, uxsock_timeout / 1000);
> -
> - if (c->cmdvec) {
> - free_keys(c->cmdvec);
> - c->cmdvec = NULL;
> - }
> -
> - if (r > 0) {
> - switch(r) {
> - case ETIMEDOUT:
> - append_strbuf_str(&c->reply, "timeout\n");
> - break;
> - case EPERM:
> - append_strbuf_str(&c->reply,
> - "permission deny: need to be root\n");
> - break;
> - default:
> - append_strbuf_str(&c->reply, "fail\n");
> - break;
> - }
> - }
> - else if (!r && get_strbuf_len(&c->reply) == 0) {
> + switch(r) {
> + case -EINVAL:
> + case -ESRCH:
> + case -ENOMEM:
get_cmdvec() returns positive errors and do_genhelp() expects positive
errors, but this expects negative errors.
> + /* return codes from get_cmdvec() */
> + genhelp_handler(c->cmd, r, &c->reply);
> + break;
> + case -EPERM:
> + append_strbuf_str(&c->reply,
> + "permission deny: need to be root\n");
> + break;
> + case -ETIMEDOUT:
> + append_strbuf_str(&c->reply, "timeout\n");
> + break;
> + case 0:
> append_strbuf_str(&c->reply, "ok\n");
> - r = 0;
> + break;
> + default:
> + append_strbuf_str(&c->reply, "fail\n");
> + break;
> }
> - /* else if (r < 0) leave *reply alone */
> - return r;
> }
>
> static void set_client_state(struct client *c, int state)
> @@ -409,6 +379,7 @@ static void set_client_state(struct client *c, int state)
> reset_strbuf(&c->reply);
> memset(c->cmd, '\0', sizeof(c->cmd));
> c->expires = ts_zero;
> + c->error = 0;
> /* fallthrough */
> case CLT_SEND:
> /* reuse these fields for next data transfer */
> @@ -420,10 +391,13 @@ static void set_client_state(struct client *c, int state)
> c->state = state;
> }
>
> -static void handle_client(struct client *c, void *trigger_data)
> +static void handle_client(struct client *c, struct vectors *vecs)
> {
> ssize_t n;
>
> + condlog(4, "%s: cli[%d] state=%d cmd=\"%s\" repl \"%s\"", __func__,
> + c->fd, c->state, c->cmd, get_strbuf_str(&c->reply));
> +
> switch (c->state) {
> case CLT_RECV:
> if (c->cmd_len == 0) {
> @@ -464,15 +438,52 @@ static void handle_client(struct client *c, void *trigger_data)
> return;
> set_client_state(c, CLT_PARSE);
> }
> - break;
> - default:
> - break;
> - }
> + condlog(4, "cli[%d]: Got request [%s]", c->fd, c->cmd);
> + /* fallthrough */
>
> - condlog(4, "cli[%d]: Got request [%s]", c->fd, c->cmd);
> - uxsock_trigger(c, trigger_data);
> + case CLT_PARSE:
Since you already print this information at the top of the function, it
seems liek it would make more sense to put these prints before the
followthroughs, so that they get double printed immediately when the
function is called for devices not in CLT_RECV.
> + condlog(4, "%s: cli[%d] state=%d cmd=\"%s\" repl \"%s\"", __func__,
> + c->fd, c->state, c->cmd, get_strbuf_str(&c->reply));
> + c->error = parse_cmd(c);
> +
> + /* Permission check */
> + if (c->error == 0 && c->cmdvec && VECTOR_SIZE(c->cmdvec) > 0) {
> + struct key *kw = VECTOR_SLOT(c->cmdvec, 0);
> +
> + if (!c->is_root && kw->code != LIST) {
> + /* this will fall through to CLT_SEND */
> + c->error = -EPERM;
> + condlog(0, "%s: cli[%d]: unauthorized cmd \"%s\"",
> + __func__, c->fd, c->cmd);
> + }
> + }
> + set_client_state(c, CLT_WAIT_LOCK);
I don't have strong feelings about this, but this state machine doesn't
want to always fall through. sometimes, like if you get -EPERM, you want
to swith from CLT_PARSE to CLT_SEND. If instead of fallthroughs, you
just put the switch statement in a loop, and simply returned when you
wanted to break out to uxsock_listen, you could jump from any state to
any other state, and wouldn't need to have code to skip the actions of
some states, to enable the follow throughs. Just a thought.
-Ben
> + /* fallthrough */
> +
> + case CLT_WAIT_LOCK:
> + condlog(4, "%s: cli[%d] state=%d cmd=\"%s\" repl \"%s\"", __func__,
> + c->fd, c->state, c->cmd, get_strbuf_str(&c->reply));
> + /* tbd */
> + set_client_state(c, CLT_WORK);
> + /* fallthrough */
> +
> + case CLT_WORK:
> + condlog(4, "%s: cli[%d] state=%d cmd=\"%s\" repl \"%s\"", __func__,
> + c->fd, c->state, c->cmd, get_strbuf_str(&c->reply));
> + if (c->error == 0 && c->handler)
> + c->error = execute_handler(c, vecs, uxsock_timeout / 1000);
> +
> + if (c->cmdvec) {
> + free_keys(c->cmdvec);
> + c->cmdvec = NULL;
> + }
> + set_client_state(c, CLT_SEND);
> + /* fallthrough */
> +
> + case CLT_SEND:
> + if (get_strbuf_len(&c->reply) == 0)
> + default_reply(c, c->error);
>
> - if (get_strbuf_len(&c->reply) > 0) {
> const char *buf = get_strbuf_str(&c->reply);
>
> if (send_packet(c->fd, buf) != 0)
> @@ -481,9 +492,13 @@ static void handle_client(struct client *c, void *trigger_data)
> condlog(4, "cli[%d]: Reply [%zu bytes]", c->fd,
> get_strbuf_len(&c->reply) + 1);
> reset_strbuf(&c->reply);
> - }
>
> - set_client_state(c, CLT_RECV);
> + set_client_state(c, CLT_RECV);
> + break;
> +
> + default:
> + break;
> + }
> }
>
> /*
> --
> 2.33.0
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