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util: don't re-add the qdisc used for tx filters if it already exists

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There will soon be two separate users of tc on virtual networks, and
both will use the "qdisc root handle 1: htb" to add tx filters. One or the
other could get the first chance to add the qdisc, and then if at a
later time the other decides to use it, we need to prevent the 2nd
user from attempting to re-add the qdisc (because that just generates
an error).

We do this by running "tc qdisc show dev $bridge handle 1:" then
checking if the output of that command contains both "qdisc" and " 1:
".[*] If it does then the qdisc has already been added. If not then we
need to add it now.

[*]As of this writing, the output more exactly starts with "qdisc
htb 1: root", but our comparison is made purposefully generous to
increase the chances that it will continue to work properly if tc
modifies the format of its output.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
This commit is contained in:
Laine Stump 2024-11-25 22:24:47 -05:00 committed by Michal Privoznik
parent 35a5bf25d1
commit f1d94bbfa6
2 changed files with 32 additions and 6 deletions
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35
src/util/virnetdevbandwidth.c
View File

@ -805,12 +805,35 @@ int
virNetDevBandWidthAddTxFilterParentQdisc(const char *ifname,
bool hierarchical_class)
{
g_autoptr(virCommand) cmd = NULL;
g_autoptr(virCommand) testCmd = NULL;
g_autofree char *testResult = NULL;
cmd = virCommandNew(TC);
virCommandAddArgList(cmd, "qdisc", "add", "dev", ifname, "root",
"handle", "1:", "htb", "default",
hierarchical_class ? "2" : "1", NULL);
/* first check it the qdisc with handle 1: was already added for
* this interface by someone else
*/
testCmd = virCommandNew(TC);
virCommandAddArgList(testCmd, "qdisc", "show", "dev", ifname,
"handle", "1:", NULL);
virCommandSetOutputBuffer(testCmd, &testResult);
return virCommandRun(cmd, NULL);
if (virCommandRun(testCmd, NULL) < 0)
return -1;
/* output will be something like: "qdisc htb 1: root refcnt ..."
* if the qdisc was already added. We just search for "qdisc" and
* " 1: " anywhere in the output to allow for tc changing its
* output format.
*/
if (!(testResult && strstr(testResult, "qdisc") && strstr(testResult, " 1: "))) {
/* didn't find qdisc in output, so we need to add one */
g_autoptr(virCommand) addCmd = virCommandNew(TC);
virCommandAddArgList(addCmd, "qdisc", "add", "dev", ifname, "root",
"handle", "1:", "htb", "default",
hierarchical_class ? "2" : "1", NULL);
return virCommandRun(addCmd, NULL);
}
return 0;
}

3
tests/virnetdevbandwidthtest.c
View File

@ -147,6 +147,7 @@ mymain(void)
"</bandwidth>",
TC " qdisc del dev eth0 root\n"
TC " qdisc del dev eth0 ingress\n"
TC " qdisc show dev eth0 handle 1:\n"
TC " qdisc add dev eth0 root handle 1: htb default 1\n"
TC " class add dev eth0 parent 1: classid 1:1 htb rate 1024kbps quantum 87\n"
TC " qdisc add dev eth0 parent 1:1 handle 2: sfq perturb 10\n"
@ -177,6 +178,7 @@ mymain(void)
"</bandwidth>",
TC " qdisc del dev eth0 root\n"
TC " qdisc del dev eth0 ingress\n"
TC " qdisc show dev eth0 handle 1:\n"
TC " qdisc add dev eth0 root handle 1: htb default 1\n"
TC " class add dev eth0 parent 1: classid 1:1 htb rate 1kbps ceil 2kbps burst 4kb quantum 1\n"
TC " qdisc add dev eth0 parent 1:1 handle 2: sfq perturb 10\n"
@ -199,6 +201,7 @@ mymain(void)
"</bandwidth>",
TC " qdisc del dev eth0 root\n"
TC " qdisc del dev eth0 ingress\n"
TC " qdisc show dev eth0 handle 1:\n"
TC " qdisc add dev eth0 root handle 1: htb default 1\n"
TC " class add dev eth0 parent 1: classid 1:1 htb rate 4294967295kbps quantum 366503875\n"
TC " qdisc add dev eth0 parent 1:1 handle 2: sfq perturb 10\n"