Messages in this thread |  | | Subject | Re: [Re: __asm__ ] | Date | Wed, 23 May 2001 11:50:30 +0100 | From | David Howells <> |
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Okay,
"current" is a macro on i386 that expands to "get_current()". This gets the task_struct for the task currently running on the CPU executing the code.
It does this by masking out the bottom bits of its kernel stack pointer.
For example, assuming that some running process has the following task record stored in an 8KB-aligned 8KB block.
0xD520BFFF +---------------+ | | | kernel stack | | | 0xD520B498 +---- TOS ------+ <-- stack pointer: %esp | | | empty space | | | +---------------+ | | | task_struct | | | 0xD520A000 +---------------+ <-- get_current()
get_current() can work out where the base of this block is because the kernel (1) stack pointer is always within it, (2) it's aligned in memory with respect to its size:
get_current() { return %esp & ~8191; } get_current() { return 0xD520B498 & 0xFFFFE000; } get_current() = 0xD520A000
So "current->fs" is a structure that holds the current task's idea of its root filesystem (chroot), current working directory (chdir) and current umask.
And so "current->fs->root" is the task's filesystem root dentry.
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