poky/meta/recipes-support/bmap-tools/files/0002-CLI.py-fix-block-device-udev-race-condition.patch

From 34f4321dfce28697f830639260076e60d765698b Mon Sep 17 00:00:00 2001
From: Trevor Woerner <twoerner@gmail.com>
Date: Fri, 12 Jan 2024 01:16:19 -0500
Subject: [PATCH 2/3] CLI.py: fix block device udev race condition

We are encouraged to add a udev rule to change a block device's
bdi/max_ratio to '1' and queue/scheduler to 'none', which I did.
So I was surprised when, about 50% of the time, I kept seeing:

	...
	bmaptool: info: failed to enable I/O optimization, expect suboptimal speed (reason: cannot switch to the 'none' I/O scheduler: 'bfq' in use. [Errno 13] Permission denied: '/sys/dev/block/8:160/queue/scheduler')
	bmaptool: info: You may want to set these I/O optimizations through a udev rule like this:
	...

The strange part is that sometimes it doesn't report a problem and
sometimes it does, even if the block device is left plugged in continuously
between multiple bmaptool invocations.

In all of my tests the bdi/max_ratio is always okay, but the
queue/scheduler would sometimes be reported as being the default scheduler,
not the one the udev rule was setting (none). Yet no matter how many times
I would read the file outside of bmaptool it always would be set to the
correct scheduler.

It turns out that opening a block device in "wb+" mode, which is what
bmaptool is doing at one point, causes the block device to act as though
it was just inserted, giving it the default settings, then causing udev to
trigger to switch it to the requested settings. However, if udev doesn't
finish before bmaptool reads the scheduler value there's a chance it will
read the pre-udev value, not the post-udev value, even though the block
device was never physically removed and re-inserted.

bmaptool was opening every file, then checking for block devices and
if found, closing then re-opening the block devices via a special
block-opening helper function. This patch re-organizes the code to only
open block devices once using the special block-opening helper function
that does not open block devices in "wb+" mode.

Upstream-Status: Submitted [https://github.com/intel/bmap-tools/pull/130]
Signed-off-by: Trevor Woerner <twoerner@gmail.com>
---
 bmaptools/CLI.py | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/bmaptools/CLI.py b/bmaptools/CLI.py
index 82303b7bc398..0a263f05cf43 100644
--- a/bmaptools/CLI.py
+++ b/bmaptools/CLI.py
@@ -38,6 +38,7 @@ import tempfile
 import traceback
 import shutil
 import io
+import pathlib
 from bmaptools import BmapCreate, BmapCopy, BmapHelpers, TransRead
 
 VERSION = "3.7"
@@ -440,17 +441,16 @@ def open_files(args):
     # Try to open the destination file. If it does not exist, a new regular
     # file will be created. If it exists and it is a regular file - it'll be
     # truncated. If this is a block device, it'll just be opened.
+    dest_is_blkdev = False
     try:
-        dest_obj = open(args.dest, "wb+")
+        if pathlib.Path(args.dest).is_block_device():
+            dest_is_blkdev = True
+            dest_obj = open_block_device(args.dest)
+        else:
+            dest_obj = open(args.dest, "wb+")
     except IOError as err:
         error_out("cannot open destination file '%s':\n%s", args.dest, err)
 
-    # Check whether the destination file is a block device
-    dest_is_blkdev = stat.S_ISBLK(os.fstat(dest_obj.fileno()).st_mode)
-    if dest_is_blkdev:
-        dest_obj.close()
-        dest_obj = open_block_device(args.dest)
-
     return (image_obj, dest_obj, bmap_obj, bmap_path, image_obj.size, dest_is_blkdev)
 
 
-- 
2.43.0.76.g1a87c842ece3