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RE: second call to mmap() results in error
- From: "Lavrentiev, Anton (NIH/NLM/NCBI) [C]" <lavr at ncbi dot nlm dot nih dot gov>
- To: "cygwin at cygwin dot com" <cygwin at cygwin dot com>
- Date: Thu, 30 Jan 2014 19:46:31 +0000
- Subject: RE: second call to mmap() results in error
- Authentication-results: sourceware.org; auth=none
- References: <20140129181250 dot GW2821 at calimero dot vinschen dot de> <52E95786 dot 8050606 at gmail dot com> <20140130095822 dot GY2821 at calimero dot vinschen dot de> <001801cf1db6$66c47c40$344d74c0$ at lbmsys dot com> <20140130124558 dot GA2821 at calimero dot vinschen dot de> <003801cf1dbd$fc3ffc70$f4bff550$ at lbmsys dot com> <20140130170142 dot GD2821 at calimero dot vinschen dot de> <5F8AAC04F9616747BC4CC0E803D5907D0C4763CC at MLBXv04 dot nih dot gov> <52EA9A53 dot 2050203 at cygwin dot com> <5F8AAC04F9616747BC4CC0E803D5907D0C4764C5 at MLBXv04 dot nih dot gov> <20140130183956 dot GA3573 at ednor dot casa dot cgf dot cx> <5F8AAC04F9616747BC4CC0E803D5907D0C4764ED at MLBXv04 dot nih dot gov> <52EA9EA2 dot 5030202 at cygwin dot com> <5F8AAC04F9616747BC4CC0E803D5907D0C476528 at MLBXv04 dot nih dot gov> <52EAA171 dot 406 at cygwin dot com> <5F8AAC04F9616747BC4CC0E803D5907D0C4765D8 at MLBXv04 dot nih dot gov> <52EAA848 dot 7070808 at cygwin dot com>
> So if the question is why do you need to include ftruncate() in the code,
> take a look here:
No, that was not the question. W/o ftruncate(), _referencing_ the memory
becomes a problem (and the original code did not do that, but simply mmap'ed
two files).
> > Adding the <unistd.h> fixes the problem in all its iterations
OP privately wrote:
> The problem is also fixed by correct type-casting in the calls to mmap() ...
>
> mmap1 = mmap(NULL, (size_t) 524304, PROT_WRITE | PROT_READ, MAP_SHARED,
> shm_fd1, 0);
>
> The address returned from the call to mmap() -- with or without the
> ftruncate() -- was bad without the (size_t) specification.
(note "with or without ftruncate()")
And I ask again (last time, I promise), how on Earth adding <unistd.h> to
the code below would make the code suddenly working? (Like I said before,
that code worked for me, with -Wall showing nothing, from the very beginning.)
Anton Lavrentiev
Contractor NIH/NLM/NCBI
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/errno.h>
#include <fcntl.h>
#include <sys/mman.h>
int main()
{
int shm_fd1, shm_fd2;
char *mmap1, *mmap2;
/* get fd for each block of memory */
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);
}
shm_fd2 = shm_open("/block2", O_CREAT | O_RDWR, 0666);
if (shm_fd2 == -1) {
fprintf(stderr, "Couldn't get fd for /UNI_queue (%s)\n",
strerror(errno));
exit(1);
}
/* map each block */
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);
}
mmap2 = mmap(NULL, 524304, PROT_WRITE | PROT_READ, MAP_SHARED, shm_fd2,
0);
if (mmap2 == (char *)-1) {
fprintf(stderr, "Couldn't map memory for /block2 (%s)\n",
strerror(errno));
exit(1);
}
fprintf(stdout, "Shared memory initialized\n");
exit(0);
}
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