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authorDavid Howells <dhowells@redhat.com>2006-09-27 01:50:22 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-27 08:26:15 -0700
commit930e652a21a08986b03d1f370f933057dc0db2dc (patch)
treec422f35bc2e7c17f58cb14544919affa52d8bac6 /Documentation/nommu-mmap.txt
parent0112c4c6461fed12ed9bcb249f967bc17a23f6c4 (diff)
downloadlinux-930e652a21a08986b03d1f370f933057dc0db2dc.tar.gz
[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: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation/nommu-mmap.txt')
-rw-r--r--Documentation/nommu-mmap.txt10
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/nommu-mmap.txt b/Documentation/nommu-mmap.txt
index 4db7c18bf68..7714f57caad 100644
--- a/Documentation/nommu-mmap.txt
+++ b/Documentation/nommu-mmap.txt
@@ -138,6 +138,16 @@ mode. The former through the usual mechanism, the latter through files created
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
=============