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Commit 930e652a authored by David Howells's avatar David Howells Committed by Linus Torvalds
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[PATCH] NOMMU: Make futexes work under NOMMU conditions 



Make futexes work under NOMMU conditions.

This can be tested by running this in one shell:

	#define SYSERROR(X, Y) \
		do { if ((long)(X) == -1L) { perror(Y); exit(1); }} while(0)

	int main()
	{
		int shmid, tmp, *f, n;

		shmid = shmget(23, 4, IPC_CREAT|0666);
		SYSERROR(shmid, "shmget");

		f = shmat(shmid, NULL, 0);
		SYSERROR(f, "shmat");

		n = *f;
		printf("WAIT: %p{%x}\n", f, n);
		tmp = futex(f, FUTEX_WAIT, n, NULL, NULL, 0);
		SYSERROR(tmp, "futex");
		printf("WAITED: %d\n", tmp);

		tmp = shmdt(f);
		SYSERROR(tmp, "shmdt");

		exit(0);
	}

And then this in the other shell:

	#define SYSERROR(X, Y) \
		do { if ((long)(X) == -1L) { perror(Y); exit(1); }} while(0)

	int main()
	{
		int shmid, tmp, *f;

		shmid = shmget(23, 4, IPC_CREAT|0666);
		SYSERROR(shmid, "shmget");

		f = shmat(shmid, NULL, 0);
		SYSERROR(f, "shmat");

		(*f)++;
		printf("WAKE: %p{%x}\n", f, *f);
		tmp = futex(f, FUTEX_WAKE, 1, NULL, NULL, 0);
		SYSERROR(tmp, "futex");
		printf("WOKE: %d\n", tmp);

		tmp = shmdt(f);
		SYSERROR(tmp, "shmdt");

		exit(0);
	}

The first program will set up a SYSV IPC SHM segment and wait on a futex in it
for the number at the start to change.  The program will increment that number
and wake the first program up.  This leads to output of the form:

	SHELL 1			SHELL 2
	=======================	=======================
	# /dowait
	WAIT: 0xc32ac000{0}
				# /dowake
				WAKE: 0xc32ac000{1}
	WAITED: 0		WOKE: 1

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 0112c4c6

Documentation/nommu-mmap.txt

+10 −0
Original line number Original line Diff line number Diff line
@@ -138,6 +138,16 @@ mode. The former through the usual mechanism, the latter through files created 
on ramfs or tmpfs mounts.

on ramfs or tmpfs mounts.









=======

FUTEXES

=======



Futexes are supported in NOMMU mode if the arch supports them.  An error will

be given if an address passed to the futex system call lies outside the

mappings made by a process or if the mapping in which the address lies does not

support futexes (such as an I/O chardev mapping).





=============

=============

NO-MMU MREMAP

NO-MMU MREMAP

=============

=============

mm/nommu.c

+9 −5
Original line number Original line Diff line number Diff line
@@ -349,6 +349,15 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) 
}

}

EXPORT_SYMBOL(find_vma);

EXPORT_SYMBOL(find_vma);





/*

 * find a VMA

 * - we don't extend stack VMAs under NOMMU conditions

 */

struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr)

{

	return find_vma(mm, addr);

}



/*

/*

 * look up the first VMA exactly that exactly matches addr

 * look up the first VMA exactly that exactly matches addr

 * - should be called with mm->mmap_sem at least held readlocked

 * - should be called with mm->mmap_sem at least held readlocked
@@ -1153,11 +1162,6 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, 
	return NULL;

	return NULL;

}

}





struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr)

{

	return NULL;

}



int remap_pfn_range(struct vm_area_struct *vma, unsigned long from,

int remap_pfn_range(struct vm_area_struct *vma, unsigned long from,

		unsigned long to, unsigned long size, pgprot_t prot)

		unsigned long to, unsigned long size, pgprot_t prot)

{

{