what does a number of "_" mean?

[Shinpei Kato <shinny@j02.itscom.net>]

Pls look over my recent increasing askings.
I'm studying the internal of the linux kernel for my university task.
To study it effectively, I think I have to know the way to name
types, variables and functions. Especially, I wanna know what a number
of "_" at the beginning of name means.
For instance, on codes about process, the type __wait_queue has two "_"s
at the beginning. What does it mean? Also the function __switch_to() has
two. Meanwhile the function _exit() has one "_".

Could someone tell me the way to name these?

Regards,

-- 
Shinpei Kato <shinny@j02.itscom.net>

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