[PATCH v4 1/7] x86/resctrl: Add multiple tasks to the resctrl group at once

[Babu Moger]

The resctrl task assignment for MONITOR or CONTROL group needs to be
done one at a time. For example:

  $mount -t resctrl resctrl /sys/fs/resctrl/
  $mkdir /sys/fs/resctrl/clos1
  $echo 123 > /sys/fs/resctrl/clos1/tasks
  $echo 456 > /sys/fs/resctrl/clos1/tasks
  $echo 789 > /sys/fs/resctrl/clos1/tasks

This is not user-friendly when dealing with hundreds of tasks.

It can be improved by supporting the multiple task id assignment in
one command with the tasks separated by commas. For example:

  $echo 123,456,789 > /sys/fs/resctrl/clos1/tasks

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
 Documentation/x86/resctrl.rst          |    9 ++++++++-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |   31 ++++++++++++++++++++++++++++++-
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/Documentation/x86/resctrl.rst b/Documentation/x86/resctrl.rst
index 387ccbcb558f..f28ed1443a6a 100644
--- a/Documentation/x86/resctrl.rst
+++ b/Documentation/x86/resctrl.rst
@@ -292,7 +292,14 @@ All groups contain the following files:
 "tasks":
 	Reading this file shows the list of all tasks that belong to
 	this group. Writing a task id to the file will add a task to the
-	group. If the group is a CTRL_MON group the task is removed from
+	group. Multiple tasks can be added by separating the task ids
+	with commas. Tasks will be assigned sequentially in the order it
+	is entered. Failures while assigning the tasks will be aborted
+	immediately and tasks next in the sequence will not be assigned.
+	Users may need to retry them again. Failure details possibly with
+	pid will be logged in /sys/fs/resctrl/info/last_cmd_status file.
+
+	If the group is a CTRL_MON group the task is removed from
 	whichever previous CTRL_MON group owned the task and also from
 	any MON group that owned the task. If the group is a MON group,
 	then the task must already belong to the CTRL_MON parent of this
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 6ad33f355861..df5bd13440b0 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -696,18 +696,41 @@ static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
 				    char *buf, size_t nbytes, loff_t off)
 {
 	struct rdtgroup *rdtgrp;
+	char *pid_str;
 	int ret = 0;
 	pid_t pid;
 
-	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
+	if (nbytes == 0)
 		return -EINVAL;
+
+	buf[nbytes - 1] = '\0';
+
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
 	if (!rdtgrp) {
 		rdtgroup_kn_unlock(of->kn);
 		return -ENOENT;
 	}
+
+next:
+	if (!buf || buf[0] == '\0')
+		goto unlock;
+
 	rdt_last_cmd_clear();
 
+	pid_str = strim(strsep(&buf, ","));
+
+	if (kstrtoint(pid_str, 0, &pid)) {
+		rdt_last_cmd_printf("Task list parsing error\n");
+		ret = -EINVAL;
+		goto unlock;
+	}
+
+	if (pid < 0) {
+		rdt_last_cmd_printf("Invalid pid %d value\n", pid);
+		ret = -EINVAL;
+		goto unlock;
+	}
+
 	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED ||
 	    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
 		ret = -EINVAL;
@@ -716,6 +739,12 @@ static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
 	}
 
 	ret = rdtgroup_move_task(pid, rdtgrp, of);
+	if (ret) {
+		rdt_last_cmd_printf("Error while processing task %d\n", pid);
+		goto unlock;
+	} else {
+		goto next;
+	}
 
 unlock:
 	rdtgroup_kn_unlock(of->kn);