Managing NVMe subsystem I/O policies in Linux:

1. get_nvme_subsystem_io_policy(subsystem): This function reads the
current I/O policy for a specified NVMe subsystem from the
/sys/class/nvme-subsystem/<subsystem>/iopolicy file and returns it
as a string. It uses the process.run() function to execute the
cat command with sudo privileges and ignores the command's status.
2. change_nvme_subsystem_io_policy(subsystem, io_policy):
This function changes the I/O policy of an NVMe subsystem to the
specified policy. It first checks if the current policy matches the
desired policy and returns True if they are the same. If not,
it executes the echo command to set the new policy. The function
raises a NvmeException if the command fails and returns True
if the policy was changed successfully.

Both functions use the process.run() function from the process module
to execute shell commands with sudo privileges and ignore their status.
The get_nvme_subsystem_io_policy() function does not take any action
if the current policy matches the desired policy, while the
change_nvme_subsystem_io_policy() function raises an exception or
returns True based on the outcome of the policy change.

Signed-off-by: Maram Srimannarayana Murthy <[email protected]>

Author: maramsmurthy

avocado/utils/nvme.py

@@ -529,3 +529,39 @@ def get_subsystem_using_ctrl_name(ctrl):
         if ctrl in ctrls:
             return get_subsys_name_with_nqn(device_nqn)
     return ""
+
+
+def get_nvme_subsystem_io_policy(subsystem):
+    """
+    Read io policy parameter from sysfs folder and returns a string
+
+    :param subsystem: Name of the subsystem
+    :rtype: String
+    """
+    cmd = f"cat /sys/class/nvme-subsystem/{subsystem}/iopolicy"
+    return process.run(
+        cmd, shell=True, sudo=True, ignore_status=True
+    ).stdout_text.strip()
+
+
+def change_nvme_subsystem_io_policy(subsystem, io_policy):
+    """
+    Changes io policy of nvme device to specified io policy
+    Change in io policy is not persistent
+
+    :param subsystem: Name of the subsystem
+    :param io_policy: Name of the io_policy to which we want to set
+    :raises: NvmeException on command failures
+    :rtype: Boolean
+    """
+    cmd = f"echo {io_policy} > /sys/class/nvme-subsystem/{subsystem}/iopolicy"
+    if get_nvme_subsystem_io_policy(subsystem) == io_policy:
+        LOGGER.info("Returning True as iopolicy is same as current")
+        return True
+    if process.system(cmd, shell=True, sudo=True, ignore_status=True):
+        raise NvmeException(f"Changing nvme subsystem iopolicy is failed: {cmd}")
+    cmd = f"cat /sys/class/nvme-subsystem/{subsystem}/iopolicy"
+    output = process.run(
+        cmd, shell=True, sudo=True, ignore_status=True
+    ).stdout_text.strip()
+    return output == io_policy