site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com On Apr 11, 2006, at 11:47 AM, Roberto Toro wrote: I'm trying to make some processes share a quite large block of memory (~8MB). I started using shmget(). It worked well for files ~800KB but not for 8MB. So I moved to shm_open() and mmap(), and now I can't allocate more than a single page of memory, 4096 bytes !! This code shows the problem: [ ... ] off_t len = 4096; #include <stdio.h> #include <errno.h> #include <sys/mman.h> #include <fcntl.h> #include <unistd.h> #include <string.h> int main(__unused int argc, __unused char *argv[]) { int err, fd; off_t len = 4097; char *shm; fd = shm_open("/1234",O_CREAT|O_RDWR|O_EXCL,0666); if(fd<0) printf("shm_open() failed: %s\n",strerror(errno)); err = ftruncate(fd,len); if(err<0) printf("ftruncate() failed: %s\n",strerror(errno)); shm = mmap(NULL,len,PROT_READ|PROT_WRITE,MAP_SHARED,fd,(off_t)0); err = munmap(shm,len); if(err<0) printf("munmap() failed: %s\n",strerror(errno)); err = shm_unlink("/1234"); if(err<0) printf("shm_unlink() failed: %s\n",strerror(errno)); err = close(fd); if(err<0) printf("clos() failed: %s\n",strerror(errno)); return 0; } -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... size_t len=4096; Any help/hint/code-snippet will be *very* appreciated. It's unreported compilation warnings that are biting you; the minimum change required is: since the length argument to mmap() and ftruncate() is an off_t (64 bits), not a size_t (32 bits). The variable fails to be automatically coerced because you don't have the ftruncate() prototype in scope, since you failed to include <unistd.h>. You should also include <string.h> for the prototype for the strerror() function. Here are the warning flags I tend to use when compiling my own code to catch things like this in the compiler: CFLAGS= -Wall -Wno-format-y2k -W -Wstrict-prototypes -Wmissing- prototypes \ -Wpointer-arith -Wreturn-type -Wcast-qual -Wwrite-strings - Wswitch \ -Wshadow -Wcast-align -Wbad-function-cast -Wchar-subscripts -Winline \ -Wnested-externs -Wredundant-decls -Werror The last option makes warnings a fatal compilation error; in this case, you'd also need to have <sys/cdefs.h> (which is pretty much automatic) and add the __unused attribute before the argc/argv parameter declarations, since your code doesn't use them. Here's a compilation warning free version of the code that works like you want it to work: /* * technically MAP_FAILED should be compared here, instead of (char *)-1; * but I'm not sure if it's defined in the <sys/mman.h> header in your * version of the SDK that you're using here. */ if (shm==(char*)-1) printf("mmap() failed: %s\n",strerror(errno)); This email sent to site_archiver@lists.apple.com