[libvirt] [Qemu-devel] [PATCH v3 2/5] qapi: Add pass-fd QMP command
Luiz Capitulino
lcapitulino at redhat.com
Fri Jun 15 15:14:25 UTC 2012
On Fri, 15 Jun 2012 11:04:16 -0400
Corey Bryant <coreyb at linux.vnet.ibm.com> wrote:
>
>
> On 06/15/2012 10:32 AM, Luiz Capitulino wrote:
> > On Thu, 14 Jun 2012 11:55:02 -0400
> > Corey Bryant <coreyb at linux.vnet.ibm.com> wrote:
> >
> >> This patch adds the pass-fd QMP command using the QAPI framework.
> >> Like the getfd command, it is used to pass a file descriptor via
> >> SCM_RIGHTS. However, the pass-fd command also returns the received
> >> file descriptor, which is a difference in behavior from the getfd
> >> command, which returns nothing.
> >>
> >> The closefd command can be used to close a file descriptor that was
> >> passed with the pass-fd command.
> >>
> >> Note that when using getfd or pass-fd, there are some commands
> >> (e.g. migrate with fd:name) that implicitly close the named fd.
> >> When this is not the case, closefd must be used to avoid fd leaks.
> >>
> >> Signed-off-by: Corey Bryant <coreyb at linux.vnet.ibm.com>
> >> ---
> >> v2:
> >> -Introduce new QMP command to pass/return fd (lcapitulino at redhat.com)
> >> -Use passfd as command name (berrange at redhat.com)
> >>
> >> v3:
> >> -Use pass-fd as command name (lcapitulino at redhat.com)
> >> -Fail pass-fd if fdname already exists (lcapitulino at redhat.com)
> >> -Add notes to QMP command describing behavior in more detail
> >> (lcapitulino at redhat.com, eblake at redhat.com)
> >> -Add note about fd leakage (eblake at redhat.com)
> >>
> >> monitor.c | 33 +++++++++++++++++++++++++++++++++
> >> qapi-schema.json | 19 +++++++++++++++++++
> >> qmp-commands.hx | 34 ++++++++++++++++++++++++++++++++++
> >> 3 files changed, 86 insertions(+)
> >>
> >> diff --git a/monitor.c b/monitor.c
> >> index 1a7f7e7..6d99368 100644
> >> --- a/monitor.c
> >> +++ b/monitor.c
> >> @@ -2182,6 +2182,39 @@ static void do_inject_mce(Monitor *mon, const QDict *qdict)
> >> }
> >> #endif
> >>
> >> +int64_t qmp_pass_fd(const char *fdname, Error **errp)
> >> +{
> >> + mon_fd_t *monfd;
> >> + int fd;
> >> +
> >> + fd = qemu_chr_fe_get_msgfd(cur_mon->chr);
> >> + if (fd == -1) {
> >> + error_set(errp, QERR_FD_NOT_SUPPLIED);
> >> + return -1;
> >> + }
> >> +
> >> + if (qemu_isdigit(fdname[0])) {
> >> + error_set(errp, QERR_INVALID_PARAMETER_VALUE, "fdname",
> >> + "a name not starting with a digit");
> >> + return -1;
> >> + }
> >> +
> >> + QLIST_FOREACH(monfd, &cur_mon->fds, next) {
> >> + if (strcmp(monfd->name, fdname) == 0) {
> >> + error_set(errp, QERR_INVALID_PARAMETER_VALUE, "fdname",
> >> + "a name that does not already exist");
> >> + return -1;
> >> + }
> >> + }
> >
> > Returning the same error class for two different errors is not a good idea.
> > I think you have two options here. You could return QERR_INVALID_PARAMETER
> > for the "already exists" case or introduce QERR_FD_EXISTS. The later is
> > certainly nicer, but we were trying to avoid having too specific errors...
> >
>
> I'm not clear on what the problem is with returning the same error class
> for two different errors. Could you explain? I don't have a problem
> changing it if it's an issue.
Because an mngt app/user won't know if what has happened was that the fd name
is invalid or if the fd name already exists.
>
> >> +
> >> + monfd = g_malloc0(sizeof(mon_fd_t));
> >> + monfd->name = g_strdup(fdname);
> >> + monfd->fd = fd;
> >
> > Maybe you could try to move this to a separate function to share code with
> > qmp_getfd()?
> >
>
> Sure, no problem. I can do that.
>
> >> +
> >> + QLIST_INSERT_HEAD(&cur_mon->fds, monfd, next);
> >> + return fd;
> >> +}
> >> +
> >> void qmp_getfd(const char *fdname, Error **errp)
> >> {
> >> mon_fd_t *monfd;
> >> diff --git a/qapi-schema.json b/qapi-schema.json
> >> index 26a6b84..ed99f23 100644
> >> --- a/qapi-schema.json
> >> +++ b/qapi-schema.json
> >> @@ -1864,6 +1864,25 @@
> >> { 'command': 'netdev_del', 'data': {'id': 'str'} }
> >>
> >> ##
> >> +# @pass-fd:
> >> +#
> >> +# Pass a file descriptor via SCM rights and assign it a name
> >> +#
> >> +# @fdname: file descriptor name
> >> +#
> >> +# Returns: The QEMU file descriptor that was received
> >> +# If file descriptor was not received, FdNotSupplied
> >> +# If @fdname is not valid, InvalidParameterType
> >> +#
> >> +# Since: 1.2.0
> >> +#
> >> +# Notes: If @fdname already exists, the command will fail.
> >> +# The 'closefd' command can be used to explicitly close the
> >> +# file descriptor when it is no longer needed.
> >> +##
> >> +{ 'command': 'pass-fd', 'data': {'fdname': 'str'}, 'returns': 'int' }
> >> +
> >> +##
> >> # @getfd:
> >> #
> >> # Receive a file descriptor via SCM rights and assign it a name
> >> diff --git a/qmp-commands.hx b/qmp-commands.hx
> >> index e3cf3c5..c039947 100644
> >> --- a/qmp-commands.hx
> >> +++ b/qmp-commands.hx
> >> @@ -869,6 +869,40 @@ Example:
> >> EQMP
> >>
> >> {
> >> + .name = "pass-fd",
> >> + .args_type = "fdname:s",
> >> + .params = "pass-fd name",
> >> + .help = "pass a file descriptor via SCM rights and assign it a name",
> >> + .mhandler.cmd_new = qmp_marshal_input_pass_fd,
> >> + },
> >> +
> >> +SQMP
> >> +pass-fd
> >> +-------
> >> +
> >> +Pass a file descriptor via SCM rights and assign it a name.
> >> +
> >> +Arguments:
> >> +
> >> +- "fdname": file descriptor name (json-string)
> >> +
> >> +Return a json-int with the QEMU file descriptor that was received.
> >> +
> >> +Example:
> >> +
> >> +-> { "execute": "pass-fd", "arguments": { "fdname": "fd1" } }
> >> +<- { "return": 42 }
> >> +
> >> +Notes:
> >> +
> >> +(1) If the name specified by the "fdname" argument already exists,
> >> + the command will fail.
> >> +(2) The 'closefd' command can be used to explicitly close the file
> >> + descriptor when it is no longer needed.
> >> +
> >> +EQMP
> >> +
> >> + {
> >> .name = "getfd",
> >> .args_type = "fdname:s",
> >> .params = "getfd name",
> >
> >
>
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