MQUERY(2) BSD System Calls Manual MQUERY(2)
mquery -- provide mapping hints to applications
mquery(void *addr, size_t len, int prot, int flags, int fd,
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(2) 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
corresponding arguments to mmap(2).
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
return 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
[ENOMEM] There was not enough memory left after the hint speci-
[EBADF] fd is not a valid open file descriptor.
The mquery() function should not be used in portable applications.
The mquery() function first appeared in OpenBSD 3.4.
BSD April 28, 2017 BSD