[PATCH v2] virsh: Allow listing just domain IDs

[Michal Privoznik]

Some completers for libvirt related tools might want to list
domain IDs only. Just like the one I've implemented for
virt-viewer [1]. I've worked around it using some awk magic,
but if it was possible to just 'virsh list --id' then I could
drop awk.

1: https://www.redhat.com/archives/virt-tools-list/2019-May/msg00014.html

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---

Diff to v1:
- Documented the new switch in the manpage
- Allowed --id to be used with --all

 docs/manpages/virsh.rst      | 21 +++++++++---------
 tools/virsh-domain-monitor.c | 42 +++++++++++++++++++++++++-----------
 2 files changed, 39 insertions(+), 24 deletions(-)

diff --git a/docs/manpages/virsh.rst b/docs/manpages/virsh.rst
index d34a1c8684..848e1a6458 100644
--- a/docs/manpages/virsh.rst
+++ b/docs/manpages/virsh.rst
@@ -621,7 +621,7 @@ list
 
    list [--inactive | --all]
         [--managed-save] [--title]
-        { [--table] | --name | --uuid }
+        { [--table] | --name | --uuid | --id }
         [--persistent] [--transient]
         [--with-managed-save] [--without-managed-save]
         [--autostart] [--no-autostart]
@@ -758,16 +758,15 @@ If *--managed-save* is specified, then domains that have managed save state
 in the listing. This flag is usable only with the default *--table* output.
 Note that this flag does not filter the list of domains.
 
-If *--name* is specified, domain names are printed instead of the table
-formatted one per line. If *--uuid* is specified domain's UUID's are printed
-instead of names. Flag *--table* specifies that the legacy table-formatted
-output should be used. This is the default.
-
-If both *--name* and *--uuid* are specified, domain UUID's and names
-are printed side by side without any header. Flag *--table* specifies
-that the legacy table-formatted output should be used. This is the
-default if neither *--name* nor *--uuid* are specified. Option
-*--table* is mutually exclusive with options *--uuid* and *--name*.
+If *--name* is specified, domain names are printed instead of the
+table formatted one per line. If *--uuid* is specified domain's UUID's
+are printed instead of names. If *--id* is specified then domain's ID's
+are printed indead of names. However, it is possible to combine
+*--name*, *--uuid* and *--id* to select only desired fields for
+printing. Flag *--table* specifies that the legacy table-formatted
+output should be used, but it is mutually exclusive with *--name*,
+*--uuid* and *--id*. This is the default and will be used if neither of
+*--name*, *--uuid* or *--id* is specified.
 
 If *--title* is specified, then the short domain description (title) is
 printed in an extra column. This flag is usable only with the default
diff --git a/tools/virsh-domain-monitor.c b/tools/virsh-domain-monitor.c
index e0491d48ac..5d0a03afa9 100644
--- a/tools/virsh-domain-monitor.c
+++ b/tools/virsh-domain-monitor.c
@@ -1919,6 +1919,10 @@ static const vshCmdOptDef opts_list[] = {
      .type = VSH_OT_BOOL,
      .help = N_("list domain names only")
     },
+    {.name = "id",
+     .type = VSH_OT_BOOL,
+     .help = N_("list domain IDs only")
+    },
     {.name = "table",
      .type = VSH_OT_BOOL,
      .help = N_("list table (default)")
@@ -1945,6 +1949,7 @@ cmdList(vshControl *ctl, const vshCmd *cmd)
     bool optTable = vshCommandOptBool(cmd, "table");
     bool optUUID = vshCommandOptBool(cmd, "uuid");
     bool optName = vshCommandOptBool(cmd, "name");
+    bool optID = vshCommandOptBool(cmd, "id");
     size_t i;
     char *title;
     char uuid[VIR_UUID_STRING_BUFLEN];
@@ -1988,8 +1993,9 @@ cmdList(vshControl *ctl, const vshCmd *cmd)
 
     VSH_EXCLUSIVE_OPTIONS("table", "name");
     VSH_EXCLUSIVE_OPTIONS("table", "uuid");
+    VSH_EXCLUSIVE_OPTIONS("table", "id");
 
-    if (!optUUID && !optName)
+    if (!optUUID && !optName && !optID)
         optTable = true;
 
     if (!(list = virshDomainListCollect(ctl, flags)))
@@ -2007,6 +2013,8 @@ cmdList(vshControl *ctl, const vshCmd *cmd)
     }
 
     for (i = 0; i < list->ndomains; i++) {
+        const char *sep = "";
+
         dom = list->domains[i];
         id = virDomainGetID(dom);
         if (id != (unsigned int) -1)
@@ -2044,20 +2052,28 @@ cmdList(vshControl *ctl, const vshCmd *cmd)
                     goto cleanup;
             }
 
-        } else if (optUUID && optName) {
-            if (virDomainGetUUIDString(dom, uuid) < 0) {
-                vshError(ctl, "%s", _("Failed to get domain's UUID"));
-                goto cleanup;
+        } else {
+            if (optUUID) {
+                if (virDomainGetUUIDString(dom, uuid) < 0) {
+                    vshError(ctl, "%s", _("Failed to get domain's UUID"));
+                    goto cleanup;
+                }
+                vshPrint(ctl, "%s", uuid);
+                sep = " ";
             }
-            vshPrint(ctl, "%-36s %-30s\n", uuid, virDomainGetName(dom));
-        } else if (optUUID) {
-            if (virDomainGetUUIDString(dom, uuid) < 0) {
-                vshError(ctl, "%s", _("Failed to get domain's UUID"));
-                goto cleanup;
+            if (optID) {
+                /* If we are asked to print IDs only then do that
+                 * only for live domains. */
+                if (id == (unsigned int) -1 && !optUUID && !optName)
+                    continue;
+                vshPrint(ctl, "%s%s", sep, id_buf);
+                sep = " ";
             }
-            vshPrint(ctl, "%s\n", uuid);
-        } else if (optName) {
-            vshPrint(ctl, "%s\n", virDomainGetName(dom));
+            if (optName) {
+                vshPrint(ctl, "%s%s", sep, virDomainGetName(dom));
+                sep = " ";
+            }
+            vshPrint(ctl, "\n");
         }
     }
 
-- 
2.26.2