| Message ID | 20160908165043.31042-1-vivien.didelot@savoirfairelinux.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Thu, 8 Sep 2016 12:50:43 -0400 Vivien Didelot <vivien.didelot@savoirfairelinux.com> wrote: > If /sbin/bridge-stp is available on the system, bridge tries to execute > it instead of the kernel implementation when starting/stopping STP. > > If anything goes wrong with /sbin/bridge-stp, bridge silently falls back > to kernel STP, making hard to debug userspace STP. > > This patch adds a br_stp_call_user helper to start/stop userspace STP > and debug errors from the program: abnormal exit status is stored in the > lower byte and normal exit status is stored in higher byte. > > Below is a simple example on a kernel with dynamic debug enabled: > > # ln -s /bin/false /sbin/bridge-stp > # brctl stp br0 on > br0: failed to start userspace STP (256) > # dmesg > br0: /sbin/bridge-stp exited with code 1 > br0: failed to start userspace STP (256) > br0: using kernel STP > > Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com> I understand that debugging STP is hard. But this solution looks like it would break existing userspace because you changed an API.
Hi Stephen, Stephen Hemminger <stephen@networkplumber.org> writes: > On Thu, 8 Sep 2016 12:50:43 -0400 > Vivien Didelot <vivien.didelot@savoirfairelinux.com> wrote: > >> If /sbin/bridge-stp is available on the system, bridge tries to execute >> it instead of the kernel implementation when starting/stopping STP. >> >> If anything goes wrong with /sbin/bridge-stp, bridge silently falls back >> to kernel STP, making hard to debug userspace STP. >> >> This patch adds a br_stp_call_user helper to start/stop userspace STP >> and debug errors from the program: abnormal exit status is stored in the >> lower byte and normal exit status is stored in higher byte. >> >> Below is a simple example on a kernel with dynamic debug enabled: >> >> # ln -s /bin/false /sbin/bridge-stp >> # brctl stp br0 on >> br0: failed to start userspace STP (256) >> # dmesg >> br0: /sbin/bridge-stp exited with code 1 >> br0: failed to start userspace STP (256) >> br0: using kernel STP >> >> Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com> > > I understand that debugging STP is hard. But this solution looks like it > would break existing userspace because you changed an API. My commit message might not be clear enough, sorry about that. This patch does not bring any functional changes. It factorizes the two calls to call_usermodehelper in a br_stp_call_user function, which prints debug messages for userspace errors if the program gets killed (e.g. ABRT) or exited with non-zero status. br_err is used if userspace STP start/stop fails, which gives direct diagnostic to the user. I can provide more example scenarios if you wish to. Thanks, Vivien
From: Vivien Didelot <vivien.didelot@savoirfairelinux.com> Date: Thu, 8 Sep 2016 12:50:43 -0400 > If /sbin/bridge-stp is available on the system, bridge tries to execute > it instead of the kernel implementation when starting/stopping STP. > > If anything goes wrong with /sbin/bridge-stp, bridge silently falls back > to kernel STP, making hard to debug userspace STP. > > This patch adds a br_stp_call_user helper to start/stop userspace STP > and debug errors from the program: abnormal exit status is stored in the > lower byte and normal exit status is stored in higher byte. > > Below is a simple example on a kernel with dynamic debug enabled: > > # ln -s /bin/false /sbin/bridge-stp > # brctl stp br0 on > br0: failed to start userspace STP (256) > # dmesg > br0: /sbin/bridge-stp exited with code 1 > br0: failed to start userspace STP (256) > br0: using kernel STP > > Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com> Applied.
diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c index 341caa0..d8ad73b 100644 --- a/net/bridge/br_stp_if.c +++ b/net/bridge/br_stp_if.c @@ -134,17 +134,36 @@ void br_stp_disable_port(struct net_bridge_port *p) br_become_root_bridge(br); } +static int br_stp_call_user(struct net_bridge *br, char *arg) +{ + char *argv[] = { BR_STP_PROG, br->dev->name, arg, NULL }; + char *envp[] = { NULL }; + int rc; + + /* call userspace STP and report program errors */ + rc = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC); + if (rc > 0) { + if (rc & 0xff) + br_debug(br, BR_STP_PROG " received signal %d\n", + rc & 0x7f); + else + br_debug(br, BR_STP_PROG " exited with code %d\n", + (rc >> 8) & 0xff); + } + + return rc; +} + static void br_stp_start(struct net_bridge *br) { - int r; - char *argv[] = { BR_STP_PROG, br->dev->name, "start", NULL }; - char *envp[] = { NULL }; struct net_bridge_port *p; + int err = -ENOENT; if (net_eq(dev_net(br->dev), &init_net)) - r = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC); - else - r = -ENOENT; + err = br_stp_call_user(br, "start"); + + if (err && err != -ENOENT) + br_err(br, "failed to start userspace STP (%d)\n", err); spin_lock_bh(&br->lock); @@ -153,9 +172,10 @@ static void br_stp_start(struct net_bridge *br) else if (br->bridge_forward_delay > BR_MAX_FORWARD_DELAY) __br_set_forward_delay(br, BR_MAX_FORWARD_DELAY); - if (r == 0) { + if (!err) { br->stp_enabled = BR_USER_STP; br_debug(br, "userspace STP started\n"); + /* Stop hello and hold timers */ del_timer(&br->hello_timer); list_for_each_entry(p, &br->port_list, list) @@ -173,14 +193,13 @@ static void br_stp_start(struct net_bridge *br) static void br_stp_stop(struct net_bridge *br) { - int r; - char *argv[] = { BR_STP_PROG, br->dev->name, "stop", NULL }; - char *envp[] = { NULL }; struct net_bridge_port *p; + int err; if (br->stp_enabled == BR_USER_STP) { - r = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC); - br_info(br, "userspace STP stopped, return code %d\n", r); + err = br_stp_call_user(br, "stop"); + if (err) + br_err(br, "failed to stop userspace STP (%d)\n", err); /* To start timers on any ports left in blocking */ mod_timer(&br->hello_timer, jiffies + br->hello_time);
If /sbin/bridge-stp is available on the system, bridge tries to execute it instead of the kernel implementation when starting/stopping STP. If anything goes wrong with /sbin/bridge-stp, bridge silently falls back to kernel STP, making hard to debug userspace STP. This patch adds a br_stp_call_user helper to start/stop userspace STP and debug errors from the program: abnormal exit status is stored in the lower byte and normal exit status is stored in higher byte. Below is a simple example on a kernel with dynamic debug enabled: # ln -s /bin/false /sbin/bridge-stp # brctl stp br0 on br0: failed to start userspace STP (256) # dmesg br0: /sbin/bridge-stp exited with code 1 br0: failed to start userspace STP (256) br0: using kernel STP Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com> --- net/bridge/br_stp_if.c | 43 +++++++++++++++++++++++++++++++------------ 1 file changed, 31 insertions(+), 12 deletions(-)