mmap() on 64 bit m/c Post: 302319767

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Operating Systems Solaris mmap() on 64 bit m/c Post 302319767 by vin_pll on Tuesday 26th of May 2009 07:13:11 AM

05-26-2009

Registered User

Sigbus with mmap.

sorry for the delayed reply,
please help me i am trying like this, though this is one sample test,
iam opening the two files one for reading and one for writing, and i am checking like this

Code:

if((input = open(argv[1], O_RDONLY)) == -1)
  fprintf(stderr, "%s: Error: opening file: %s\n", PACKAGE, argv[1]), exit(1);

 if((output = open(argv[2], O_RDWR|O_CREAT|O_TRUNC, 0666)) == -1)
  fprintf(stderr, "%s: Error: opening file: %s\n", PACKAGE, argv[2]), exit(1);

   source = (char *)mmap((char *)0, filesize, PROT_READ, MAP_SHARED,   input, 0);
printf("\n address of source==%p",source);
 if(source[0] ==-1)
  fprintf(stderr, "Error mapping input file: %s\n", argv[1]), exit(1);

target =(char *) mmap((char  *)0, filesize, PROT_WRITE, MAP_SHARED, output, 0);

printf("\n address of target==%d",target);
 if(target[0]==-1) //problem here
  fprintf(stderr, "Error mapping ouput file: %s\n", argv[2]), exit(1);

as i am opening both of them and checking instead of MAP_FAILED for the failure to target[0]==-1 ,
my question is what exactly is the data structure that mmap returns when i test for read it is successfull and for write it is not and also
if i change that to
if(target==(void*)-1 ) it returns successfull,
because in my code they have used
target[0]==-1 which is failing and results in sigbus if i replace it with
if(target==MAP_FAILED)
it is not even going for failure nor the sucess,
and fails some where in the reading. so what is the reason of sigbus
please solve my problem

vin_pll

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mmap2

MMAP2(2)						     Linux Programmer's Manual							  MMAP2(2)

NAME

       mmap2 - map files or devices into memory

SYNOPSIS

       #include <sys/mman.h>

       void *mmap2(void *addr, size_t length, int prot,
		    int flags, int fd, off_t pgoffset);

DESCRIPTION

       This  is  probably  not	the  system call that you are interested in; instead, see mmap(2), which describes the glibc wrapper function that
       invokes this system call.

       The mmap2() system call provides the same interface as mmap(2), except that the final argument  specifies  the  offset  into  the  file	in
       4096-byte  units  (instead  of  bytes, as is done by mmap(2)).  This enables applications that use a 32-bit off_t to map large files (up to
       2^44 bytes).

RETURN VALUE

       On success, mmap2() returns a pointer to the mapped area.  On error, -1 is returned and errno is set appropriately.

ERRORS

       EFAULT Problem with getting the data from user space.

       EINVAL (Various platforms where the page size is not 4096 bytes.)  offset * 4096 is not a multiple of the system page size.

       mmap2() can also return any of the errors described in mmap(2).

VERSIONS

       mmap2() is available since Linux 2.3.31.

CONFORMING TO

       This system call is Linux-specific.

NOTES

       On architectures where this system call is present, the glibc mmap() wrapper function invokes this system call rather than the mmap(2) sys-
       tem call.

       This system call does not exist on x86-64.

       On ia64, the unit for offset is actually the system page size, rather than 4096 bytes.

SEE ALSO

       getpagesize(2), mmap(2), mremap(2), msync(2), shm_open(3)

COLOPHON

       This  page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux								    2017-09-15								  MMAP2(2)