[RFC v2 PATCH 1/7] x86/resctrl: Add multiple tasks to the resctrl group at once

[Babu Moger <babu.moger@amd.com>]

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.

Improve the user experience by supporting the multiple task 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@amd.com>
---
 Documentation/x86/resctrl.rst          |    9 +++++++--
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |   24 +++++++++++++++++++++++-
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/Documentation/x86/resctrl.rst b/Documentation/x86/resctrl.rst
index 058257dc56c8..58b76fc75cb7 100644
--- a/Documentation/x86/resctrl.rst
+++ b/Documentation/x86/resctrl.rst
@@ -292,13 +292,18 @@ 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 assigned together in one command by
+	inputting the tasks separated by commas. Tasks will be assigned
+	sequentially in the order it is provided. Failure 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.
+
+	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
 	group. The task is removed from any previous MON group.
 
-
 "cpus":
 	Reading this file shows a bitmask of the logical CPUs owned by
 	this group. Writing a mask to this file will add and remove
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index e2c1599d1b37..13b7c5f3a27c 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -683,16 +683,34 @@ 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)
+	/* Valid input requires a trailing newline */
+	if (nbytes == 0 || buf[nbytes - 1] != '\n')
 		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;
+
+	pid_str = strim(strsep(&buf, ","));
+
+	if (kstrtoint(pid_str, 0, &pid) || pid < 0) {
+		rdt_last_cmd_puts("Invalid pid value\n");
+		ret = -EINVAL;
+		goto unlock;
+	}
+
 	rdt_last_cmd_clear();
 
 	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED ||
@@ -703,6 +721,10 @@ static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
 	}
 
 	ret = rdtgroup_move_task(pid, rdtgrp, of);
+	if (ret)
+		goto unlock;
+	else
+		goto next;
 
 unlock:
 	rdtgroup_kn_unlock(of->kn);