Exclusively open a device file in Linux

Question

What ways are there available, for exclusively opening a device file (say, the display frame buffer)?

[Info: I already know about flock() & friends, which have an effect only when the other applications are also using it (in other words: open() will succeed but flock() will fail if already locked) --> but still the device handle retrieved from open() can be used to write to the display..]

What about cases when I want to enforce such an exclusive access on a device files? How would such an enforcement be possible?

Thanks in advance!

Answer 1

From fcntl(2):

To make use of mandatory locks, mandatory locking must be enabled both on the filesystem that contains the file to be locked, and on the file itself.

...also, you need to enable CONFIG_MANDATORY_FILE_LOCKING in the kernel.

Mandatory locking is enabled on a filesystem using the "-o mand" option to mount(8), or the MS_MANDLOCK flag for mount(2). Mandatory locking is enabled on a file by disabling group execute permission on the file and enabling the set-group-ID permis‐ sion bit (see chmod(1) and chmod(2)).

Mandatory locking is not specified by POSIX. Some other systems also support mandatory locking, although the details of how to enable it vary across systems.

So, as you request a posix-compliant solution, the answer is: no, there is not such a feature in the POSIX standard.