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On Jan 30 07:25, Steven Bardwell wrote: > > > On 29/01/2014 19:12, Corinna Vinschen wrote: > > > >On Jan 29 09:00, Steven Bardwell wrote: > > > >>My application needs several areas of shared memory, and I am getting > > an > > > >>error ("No such device") on the second call to mmap(). The first call > > works > > > >>fine. > > > > Sorry guys, but it still works fine for me. I tried your testcase on W7 > > 32, W7 64 in 32 and 64 bit, and on Windows 8.1 64 in 32 and 64 bit. I > > tried it with Cygwin 1.7.27 and with the latest snapshot. I'm always > > getting the output "Shared memory initialized" and no error at all. > > > > > > Any chance one of you guys could debug this further, by stepping through > > the Cygwin mmap64 function, preferredly using the latest snapshot or, > > a self-built Cygwin DLL from? > > > > > > Corinna > > I reinstalled Cygwin, rebooted and the error persisted. Running 'gdb' and > stepping through the program showed that the call to mmap() fails for /block1 > also -- it is returning an invalid address. This simplification of the program > shows that error on my machine ('Bus error (core dumped)' ) occurs > when it tries to do the memcpy() to the mapped address. Try this: > #include <stdio.h> > #include <stdlib.h> #include <unistd.h> > #include <string.h> > #include <sys/types.h> > #include <sys/errno.h> > #include <fcntl.h> > #include <sys/mman.h> > > int main() > { > int shm_fd1; > char *mmap1; > shm_fd1 = shm_open("/block1", O_CREAT | O_RDWR, 0666); > if (shm_fd1 == -1) { > fprintf(stderr, "Couldn't get fd for block1 (%s)\n", strerror(errno)); > exit(1); > } > ftruncate(shm_fd1, 524304); > mmap1 = mmap(NULL, 524304, PROT_WRITE | PROT_READ, MAP_SHARED, shm_fd1, 0); > if (mmap1 == (char *)-1) { > fprintf(stderr, "Couldn't map memory for /block1 (%s)\n", strerror(errno)); > exit(1); > } > memcpy(mmap1, "ABCDEF\0", 7); > fprintf(stdout, mmap1); > > fprintf(stdout, "Shared memory initialized\n"); > exit(0); > } The reason is that ftruncate is defined with the second argument being off_t, which is 8 byte. 524304 is an int (4 byte) only, though. Since ftruncate is declared in unistd.h, but you didn't include unistd.h, the 2nd parameter to ftruncate is auto-propagated to int, which results in an invalid new file length, and which makes ftruncate fail. Since you missed to check ftruncate's return value... you get the idea. Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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