On Thu, 14 Jun 2012 11:55:02 -0400
Corey Bryant <coreyb@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
> ---
> v2:
> -Introduce new QMP command to pass/return fd (lcapitulino@xxxxxxxxxx)
> -Use passfd as command name (berrange@xxxxxxxxxx)
>
> v3:
> -Use pass-fd as command name (lcapitulino@xxxxxxxxxx)
> -Fail pass-fd if fdname already exists (lcapitulino@xxxxxxxxxx)
> -Add notes to QMP command describing behavior in more detail
> (lcapitulino@xxxxxxxxxx, eblake@xxxxxxxxxx)
> -Add note about fd leakage (eblake@xxxxxxxxxx)
>
> 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...
> +
> + 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()?
> +
> + 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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