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docs/devel: update error handling guidance for HMP commands 

Best practice is to use the 'hmp_handle_error' function, not
'monitor_printf' or 'error_report_err'. This ensures that the
message always gets an 'Error: ' prefix, distinguishing it
from normal command output.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
This commit is contained in:
Daniel P. Berrangé 2021-10-28 16:13:55 +01:00
parent fa2613afa1
commit 6fa6b54f5b
1 changed files with 7 additions and 12 deletions
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19
docs/devel/writing-monitor-commands.rst
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@ -293,9 +293,7 @@ Here's the implementation of the "hello-world" HMP command::
Error *err = NULL;
qmp_hello_world(!!message, message, &err);
if (err) {
monitor_printf(mon, "%s\n", error_get_pretty(err));
error_free(err);
if (hmp_handle_error(mon, err)) {
return;
}
}
@ -307,9 +305,10 @@ There are three important points to be noticed:
1. The "mon" and "qdict" arguments are mandatory for all HMP functions. The
former is the monitor object. The latter is how the monitor passes
arguments entered by the user to the command implementation
2. hmp_hello_world() performs error checking. In this example we just print
the error description to the user, but we could do more, like taking
different actions depending on the error qmp_hello_world() returns
2. hmp_hello_world() performs error checking. In this example we just call
hmp_handle_error() which prints a message to the user, but we could do
more, like taking different actions depending on the error
qmp_hello_world() returns
3. The "err" variable must be initialized to NULL before performing the
QMP call
@ -466,9 +465,7 @@ Here's the HMP counterpart of the query-alarm-clock command::
Error *err = NULL;
clock = qmp_query_alarm_clock(&err);
if (err) {
monitor_printf(mon, "Could not query alarm clock information\n");
error_free(err);
if (hmp_handle_error(mon, err)) {
return;
}
@ -607,9 +604,7 @@ has to traverse the list, it's shown below for reference::
Error *err = NULL;
method_list = qmp_query_alarm_methods(&err);
if (err) {
monitor_printf(mon, "Could not query alarm methods\n");
error_free(err);
if (hmp_handle_error(mon, err)) {
return;
}