Re: [libvirt] [PATCH v3 2/5] qapi: Add pass-fd QMP command

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(a)linux.vnet.ibm.com&gt; --- v2: -Introduce new QMP command to pass/return fd (lcapitulino(a)redhat.com) -Use passfd as command name (berrange(a)redhat.com) v3: -Use pass-fd as command name (lcapitulino(a)redhat.com) -Fail pass-fd if fdname already exists (lcapitulino(a)redhat.com) -Add notes to QMP command describing behavior in more detail (lcapitulino(a)redhat.com, eblake(a)redhat.com) -Add note about fd leakage (eblake(a)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; + } + }

+ + monfd = g_malloc0(sizeof(mon_fd_t)); + monfd->name = g_strdup(fdname); + monfd->fd = fd;

+ + 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",