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From: "Trent W. Buck" <trentbuck@gmail.com>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: CONFIG_UEVENT_HELPER=n kernel confuses alsactl restore
Message-ID: <20151001012623.3162.52745.reportbug@frey>
X-Mailer: reportbug 6.6.0
Date: Thu, 01 Oct 2015 11:26:23 +1000
Delivered-To: submit@bugs.debian.org

Package: alsa-utils
Version: 1.0.29-1
Severity: minor

I spotted this message when studying alsa-utils' udev rules:

    # alsactl -E HOME=/run/alsa --file /dev/null restore 0
    No state is present for card PCH
**  alsactl: sysfs_init:48: sysfs path '/sys' is invalid

    Found hardware: "HDA-Intel" "Realtek ALC662 rev3" "HDA:10ec0662,10ec0662,00100300" "0x10ec" "0x0662"
    Hardware is initialized using a generic method
    No state is present for card PCH

    # echo $?
    99

This code assumes that a working /sys will have a /sys/kernel/uevent_helper.
This is not a safe assumption in custom 3.16+ kernels.
See also https://bugs.debian.org/752742
Also /usr/share/doc/systemd/README.gz calls it a "legacy" interface,
though I think it is still essential elsewhere (e.g. busybox mdev).

    alsactl/init_sysfs.c-32-static int sysfs_init(void)
    alsactl/init_sysfs.c:46:        strlcat(sysfs_test, "/kernel/uevent_helper", sizeof(sysfs_test));
    alsactl/init_sysfs.c-47-        if (access(sysfs_test, F_OK)) {
    alsactl/init_sysfs.c-48-                error("sysfs path '%s' is invalid\n", sysfs_path);
    alsactl/init_sysfs.c-49-                return -errno;
    alsactl/init_sysfs.c-50-        }

I don't know what sysfs_init() *should* check for.

I don't know what alsactl does differently if it thinks /sys is working.

alsactl restore *does* change my mixer levels, so this might be a non-issue:

    # echo 1 >/sys/class/sound/hdaudioC0D2/reconfig
    # amixer >before
    # alsactl -E HOME=/run/alsa --file /dev/null restore 0
    [...]
    # amixer >after
    # cmp before after
    before after differ: byte 164, line 5
]