[Kimchi-devel] [PATCH v3 1/2] logical pool fixes: only list leaf devices, and read file instead of run "cat"

[Zhou Zheng Sheng]

Some devices are parent of other devices. We should just list the leaf
devices but not parent devices. For example, if a disk contains
partitions, we should only list the partitions. If a disk is held by
multipath device, we should not list the disk.

Currently we strip the last charactter from "vda1" to get "vda" and
ignore the parent "vda" device. This may fails on disk contains lots of
logical partitions, for example "vda10"'s parent is not "vda1". Another
problem is this method can not find the parent-child relation ship
between a multipath device and its slaves.

The most accurate information is on sysfs, and lsblk lists all children
device of the requested device based on sysfs. So when "lsblk -P
devices" prints only one line, it's the device itself, when it prints
more lines, they are the children devices. This patch use this method to
detect if a device a leaf one.

This patch also avoids start new "cat" process to read uevent file, it
opens the uevent file and read it directly.

v2:
  Assign string literal to constants thus avoid breaking the line.

v3:
  Save N lsblk invocations when list all devices by collecting major:min
  and device node path in one run. N is number of block devices.
  Use short-circuiting operator "and" instead of all to save extra lsblk
  invocation.

Signed-off-by: Zhou Zheng Sheng <zhshzhou at linux.vnet.ibm.com>
---
 src/kimchi/disks.py | 83 ++++++++++++++++++++++++++++++++---------------------
 1 file changed, 50 insertions(+), 33 deletions(-)

diff --git a/src/kimchi/disks.py b/src/kimchi/disks.py
index a054961..34b9e01 100644
--- a/src/kimchi/disks.py
+++ b/src/kimchi/disks.py
@@ -27,27 +27,13 @@ from kimchi.exception import OperationFailed
 from kimchi.utils import kimchi_log
 
 
-def _get_partition_path(name):
-    """ Returns device path given a partition name """
-    dev_path = None
-    maj_min = None
-
-    keys = ["NAME", "MAJ:MIN"]
-    dev_list = _get_lsblk_devs(keys)
-
-    for dev in dev_list:
-        if dev['name'] == name:
-            maj_min = dev['maj:min']
-            break
+def _get_dev_node_path(maj_min):
+    """ Returns device node path given the device number 'major:min' """
+    uevent = "/sys/dev/block/%s/uevent" % maj_min
+    with open(uevent) as ueventf:
+        content = ueventf.read()
 
-    uevent_cmd = "cat /sys/dev/block/%s/uevent" % maj_min
-    uevent = subprocess.Popen(uevent_cmd, stdout=subprocess.PIPE,
-                              stderr=subprocess.PIPE, shell=True)
-    out, err = uevent.communicate()
-    if uevent.returncode != 0:
-        raise OperationFailed("Error getting partition path for %s", name)
-
-    data = dict(re.findall(r'(\S+)=(".*?"|\S+)', out.replace("\n", " ")))
+    data = dict(re.findall(r'(\S+)=(".*?"|\S+)', content.replace("\n", " ")))
 
     return "/dev/%s" % data["DEVNAME"]
 
@@ -63,6 +49,39 @@ def _get_lsblk_devs(keys, devs=[]):
     return _parse_lsblk_output(out, keys)
 
 
+def _get_dev_major_min(name):
+    maj_min = None
+
+    keys = ["NAME", "MAJ:MIN"]
+    dev_list = _get_lsblk_devs(keys)
+
+    for dev in dev_list:
+        if dev['name'] == name:
+            maj_min = dev['maj:min']
+            break
+    else:
+        msg = "Failed to find major and minor number for %s" % name
+        raise OperationFailed(msg)
+
+    return maj_min
+
+
+def _is_dev_leaf(devNodePath):
+    try:
+        # By default, lsblk prints a device information followed by children
+        # device information
+        childrenCount = len(
+            _get_lsblk_devs(["NAME"], [devNodePath])) - 1
+    except OperationFailed as e:
+        # lsblk is known to fail on multipath devices
+        # Assume these devices contain children
+        kimchi_log.error(
+            "Error getting device info for %s: %s", devNodePath, e)
+        return False
+    else:
+        return childrenCount == 0
+
+
 def _parse_lsblk_output(output, keys):
     # output is on format key="value",
     # where key can be NAME, TYPE, FSTYPE, SIZE, MOUNTPOINT, etc
@@ -82,32 +101,30 @@ def _parse_lsblk_output(output, keys):
 
 def get_partitions_names():
     names = []
-    ignore_names = []
-    keys = ["NAME", "TYPE", "FSTYPE", "MOUNTPOINT"]
+    keys = ["NAME", "TYPE", "FSTYPE", "MOUNTPOINT", "MAJ:MIN"]
     # output is on format key="value",
     # where key can be NAME, TYPE, FSTYPE, MOUNTPOINT
     for dev in _get_lsblk_devs(keys):
         # split()[0] to avoid the second part of the name, after the
         # whiteline
         name = dev['name'].split()[0]
-        # Only list unmounted and unformated partition or disk.
-        if not all([dev['type'] in ['part', 'disk'],
-                    dev['fstype'] == "",
-                    dev['mountpoint'] == ""]):
-
-            # the whole disk must be ignored in it has at least one
-            # mounted/formatted partition
-            if dev['type'] == 'part':
-                ignore_names.append(name[:-1])
+        devNodePath = _get_dev_node_path(dev['maj:min'])
+        # Only list unmounted and unformated and leaf and (partition or disk)
+        # leaf means a partition, a disk has no partition, or a disk not held
+        # by any multipath device.
+        if not (dev['type'] in ['part', 'disk'] and
+                dev['fstype'] == "" and
+                dev['mountpoint'] == "" and
+                _is_dev_leaf(devNodePath)):
             continue
 
         names.append(name)
 
-    return list(set(names) - set(ignore_names))
+    return names
 
 
 def get_partition_details(name):
-    dev_path = _get_partition_path(name)
+    dev_path = _get_dev_node_path(_get_dev_major_min(name))
 
     keys = ["TYPE", "FSTYPE", "SIZE", "MOUNTPOINT"]
     try:
-- 
1.7.11.7