MirOS Manual: mquery(2)

MQUERY(2)                  BSD Programmer's Manual                   MQUERY(2)


     mquery - provide mapping hints to applications


     #include <sys/types.h>
     #include <sys/mman.h>

     void *
     mquery(void *addr, size_t len, int prot, int flags, int fd,
             off_t offset);


     The mquery system call checks the existing memory mappings of a process
     and returns hints to the caller about where to put a memory mapping. This
     hint can be later used when performing memory mappings with the mmap()
     system call with MAP_FIXED in the flags. The addr argument should be a
     memory location that which the caller specifies the preferred address.
     The size argument specifies the requested size of the memory area the
     caller is looking for. The fd and off arguments specify the file that
     will be mapped and the offset in it, this is the same as the correspond-
     ing arguments to mmap().

     The behavior of the function depends on the flags argument. If set to
     MAP_FIXED the pointer addr is used as a fixed hint and mquery() will re-
     turn MAP_FAILED and set errno to ENOMEM if there is not size bytes free
     after that address. Otherwise it will return the hint addr. If no flags
     are set mquery() will use addr as a starting point in memory and will
     search forward to find a memory area with size bytes free and that will
     be suitable for creating a mapping for the file and offset specified in
     the fd and off arguments. When no such area can be found mquery() will
     return and set errno to indicate the error.


     When a memory range satisfying the request is found mquery() returns the
     available address. Otherwise, MAP_FAILED is returned and errno is set to
     indicate the error.


     mquery() will fail if:

     [EINVAL]      MAP_FIXED was specified and the requested memory area is

     [ENOMEM]      There was not enough memory left after the hint specified.

     [EBADF]       fd is not a valid open file descriptor.




     The mquery() function first appeared in OpenBSD 3.4.

MirOS BSD #10-current           April 2, 2003                                1

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