Your message dated Wed, 24 Jun 2026 16:10:12 +0200
with message-id <[email protected]>
and subject line Re: Fixed upstream
has caused the Debian Bug report #1040744,
regarding v4l2loopback-dkms: Device in broken state after use with
exclusive_caps=1
to be marked as done.
This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.
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--
1040744: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1040744
Debian Bug Tracking System
Contact [email protected] with problems
--- Begin Message ---
Package: v4l2loopback-dkms
Version: 0.12.7-2
Severity: important
Tags: patch
With the Droidcam client (application to use mobile phone cameras with
the computer) the loopback device can be used only once. Then it is
neither an output nor a capture device, without being able to set format
and send data any more until the module is reloaded.
Without parameter "exclusive_caps=1" the issue doesn't appear, but I
need it for my scenario.
Output of command "v4l2-ctl -d /dev/video0 --all" before use:
Driver Info:
Driver name : v4l2 loopback
Card type : Loopback Cam
Bus info : platform:v4l2loopback-000
Driver version : 6.1.37
Capabilities : 0x85200002
Video Output
Read/Write
Streaming
Extended Pix Format
Device Capabilities
Device Caps : 0x05200002
Video Output
Read/Write
Streaming
Extended Pix Format
Output of command "v4l2-ctl -d /dev/video0 --all" after use:
Driver Info:
Driver name : v4l2 loopback
Card type : Loopback Cam
Bus info : platform:v4l2loopback-000
Driver version : 6.1.37
Capabilities : 0x85200000
Read/Write
Streaming
Extended Pix Format
Device Capabilities
Device Caps : 0x05200000
Read/Write
Streaming
Extended Pix Format
On analysis of the application no bug could be found there, but for
v4l2loopback module at the point of failure apparently
vidioc_try_fmt_cap() is called instead of vidioc_try_fmt_out(), which
must be caused by dev->ready_for_output == 0 but should be reset to 1
latest when all file handles are close.
As a VIDIOC_STREAMON ioctl is never happening here (no such call in
Droidcam), state of ready_for_output probably is changing in
v4l2_loopback_write() but without to set opener-type as WRITER at the
same time. Do I read it correctly that opener->type is unique for a
single file handle - what if the same file handle is used for both
writing and reading?
This patch fixes the issue for me:
--- v4l2loopback.c.orig 2022-08-05 00:30:07.000000000 +0200
+++ v4l2loopback.c 2023-07-10 00:25:06.480011644 +0200
@@ -2000,7 +2000,7 @@ static int v4l2_loopback_close(struct fi
v4l2_fh_exit(&opener->fh);
kfree(opener);
- if (iswriter) {
+ if (iswriter || dev->open_count.counter == 0) {
dev->ready_for_output = 1;
}
MARK();
Link to the original bug report for the Droidcam application
https://github.com/dev47apps/droidcam/issues/242
Link to similar bug report for Pyvirtualcam
https://github.com/letmaik/pyvirtualcam/issues/61
Kind regards,
Gero
-- System Information:
Debian Release: 12.0
APT prefers stable-security
APT policy: (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386
Kernel: Linux 6.1.0-10-amd64 (SMP w/4 CPU threads; PREEMPT)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled
Versions of packages v4l2loopback-dkms depends on:
ii dkms 3.0.10-8
v4l2loopback-dkms recommends no packages.
Versions of packages v4l2loopback-dkms suggests:
ii v4l2loopback-utils 0.12.7-2
-- no debconf information
--- End Message ---
--- Begin Message ---
fixed upstream.
thanks.
On Sat, 28 Feb 2026 18:34:48 +1100 Stephen Wade
<[email protected]> wrote:
This has been fixed upstream in 08639f0c which has been released as 0.14.0
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--- End Message ---
