Re: problem with mmap and cygwin 1.1.8

[Corinna Vinschen <cygwin at cygwin dot com>]

On Tue, Apr 03, 2001 at 10:02:09AM -0400, Turnbull Wallace Capt AFRL/VSBXR wrote:
> Hello all.  I've recently updated my system to cygwin 1.1.8 and gcc
> 2.95-3.2. I had been running cygwin 1.1.7 and gcc 2.95.2-6.  The following
> code (which calls mmap) worked fine under 1.1.7 but now mmap fails with
> errno = 13, "Permission denied."  (Actually, the strace shows:
> "geterrno_from_win_error: unknown windows error 1006, setting errno to 13") 
> 
> I rolled back to the previous setup just to double check and the call to
> mmap worked fine.  Attached is the broken code, some cygcheck output, and
> strace output.  I'm running Windows 2000 Pro, SP1.  I did a diff on the
> cygwin sources and noticed significant changes to mmap.cc between 1.1.7 and
> 1.1.8 but didn't I didn't delve very deep.  Any ideas?  

Your source isn't correct.

> int create_files()
> {
>    int i;
>    int fd;
>    char *p;
>    char fname[1024];
>    long size;
>    int perms;
>   
>    size = get_file_size();

At this point you get a size, probably > 0.

>    perms = 0666;
>    
>    for (i=0;i<NUMALTBINS;i++)
>    {
>       memset(fname,'\0',1024);
>       sprintf(fname,"%s/csealt%02d.map",FILEPATH,i);
>       printf("creating file %s with perms %03o\n",fname,perms);
>       
>       //create and open the file
>       if ((fd = open(fname, O_RDWR | O_CREAT | O_TRUNC, perms)) < 0)

Now you create(!) an empty(!) file.

>       {
>          fprintf(stderr,"error creating file\n");     
> 
>          return -1;      
>       }
>               
>       if ((p = mmap(0,(size_t) size, 
>               PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, fd, 0)) ==
> (caddr_t) -1)

And at this point you're trying to mmap a file with size 0 by
giving a filesize > 0.

But your example shows that the error code returned by mmap is
not correct. It should be EOVERFLOW. I will change that for the
next version.

Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Developer                                mailto:cygwin@cygwin.com
Red Hat, Inc.

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