selftests/damon/_damon_sysfs: support DAMOS quota

Patch series "selftests/damon: add more tests for core functionalities and
corner cases".

Continue DAMON selftests' test coverage improvement works with a trivial
improvement of the test code itself.  The sequence of the patches in
patchset is as follows.

The first five patches add two DAMON core functionalities tests.  Those
begins with three patches (patches 1-3) that update the test-purpose DAMON
sysfs interface wrapper to support DAMOS quota, stats, and apply interval
features, respectively.  The fourth patch implements and adds a selftest
for DAMOS quota feature, using the DAMON sysfs interface wrapper's newly
added support of the quota and the stats feature.  The fifth patch further
implements and adds a selftest for DAMOS apply interval using the DAMON
sysfs interface wrapper's newly added support of the apply interval and
the stats feature.

Two patches (patches 6 and 7) for implementing and adding two corner cases
handling selftests follow.  Those try to avoid two previously fixed bugs
from recurring.

Finally, a patch for making DAMON debugfs selftests dependency checker to
use /proc/mounts instead of the hard-coded mount point assumption follows.


This patch (of 8):

Update the test-purpose DAMON sysfs control Python module to support DAMOS
quota.

Link: https://lkml.kernel.org/r/20240207203134.69976-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20240207203134.69976-2-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/damon/_damon_sysfs.py

@@ -70,18 +70,48 @@ class DamosAccessPattern:
         if err != None:
             return err
 
+class DamosQuota:
+    sz = None                   # size quota, in bytes
+    ms = None                   # time quota
+    reset_interval_ms = None    # quota reset interval
+    scheme = None               # owner scheme
+
+    def __init__(self, sz=0, ms=0, reset_interval_ms=0):
+        self.sz = sz
+        self.ms = ms
+        self.reset_interval_ms = reset_interval_ms
+
+    def sysfs_dir(self):
+        return os.path.join(self.scheme.sysfs_dir(), 'quotas')
+
+    def stage(self):
+        err = write_file(os.path.join(self.sysfs_dir(), 'bytes'), self.sz)
+        if err != None:
+            return err
+        err = write_file(os.path.join(self.sysfs_dir(), 'ms'), self.ms)
+        if err != None:
+            return err
+        err = write_file(os.path.join(self.sysfs_dir(), 'reset_interval_ms'),
+                         self.reset_interval_ms)
+        if err != None:
+            return err
+
 class Damos:
     action = None
     access_pattern = None
-    # todo: Support quotas, watermarks, stats, tried_regions
+    quota = None
+    # todo: Support watermarks, stats, tried_regions
     idx = None
     context = None
     tried_bytes = None
 
-    def __init__(self, action='stat', access_pattern=DamosAccessPattern()):
+    def __init__(self, action='stat', access_pattern=DamosAccessPattern(),
+                 quota=DamosQuota()):
         self.action = action
         self.access_pattern = access_pattern
         self.access_pattern.scheme = self
+        self.quota = quota
+        self.quota.scheme = self
 
     def sysfs_dir(self):
         return os.path.join(
@@ -94,13 +124,7 @@ class Damos:
         err = self.access_pattern.stage()
         if err != None:
             return err
-
-        # disable quotas
-        err = write_file(os.path.join(self.sysfs_dir(), 'quotas', 'ms'), '0')
-        if err != None:
-            return err
-        err = write_file(
-                os.path.join(self.sysfs_dir(), 'quotas', 'bytes'), '0')
+        err = self.quota.stage()
         if err != None:
             return err