Getting user process pid when writing Linux Kernel Module

Question

How can I get the PID of the user process which triggered my Kernel module's file_operation.read routine (i.e., which process is reading /dev/mydev) ?

score 24 · Accepted Answer · answered Aug 11 '12 at 15:01

24

When your read function is executing, it's doing so in the context of the process that issued the system call. You should thus pe able to use current, i.e. current->pid.

answered Aug 11 '12 at 15:01

cnicutar

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what is current? read doesn't get a current as argument... ssize_t(*read) (struct file *, char __user *, size_t, loff_t *); – 0x90 Aug 11 '12 at 15:30

score 15 · Answer 2 · answered Mar 21 '13 at 07:22

These days, we have some helper functions defined in sched.h. In the case of pid, you can use:

pid = task_pid_nr(current);

to get the current task's pid.

here is the comment taken from include/linux/sched.h as of v3.8.

the helpers to get the task's different pids as they are seen from various namespaces

task_xid_nr() : global id, i.e. the id seen from the init namespace;

task_xid_vnr() : virtual id, i.e. the id seen from the pid namespace of current.

task_xid_nr_ns() : id seen from the ns specified;

set_task_vxid() : assigns a virtual id to a task;

see also pid_nr() etc in include/linux/pid.h

score 5 · Answer 3 · answered Apr 25 '13 at 23:33

On a kernel 2.6.39 arm build, if current->pid does not work then it may be done by:

    pid_nr(get_task_pid(current, PIDTYPE_PID))

The PIDTYPE_PID can be substituted by PIDTYPE_PGID or PIDTYPE_SID. The header source is at include/linux/pid.h as Yasushi pointed out.

Which of the approaches work depends on what header files the code uses.

Getting user process pid when writing Linux Kernel Module

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