|MMAP(2)||System Calls Manual||MMAP(2)|
*addr, size_t len,
mmapfunction causes the pages starting at addr and continuing for at most len bytes to be mapped from the object described by fd, starting at byte offset offset. If offset or len is not a multiple of the pagesize, the mapped region may extend past the specified range.
If addr is non-zero, it is used as a hint to the system. (As a convenience to the system, the actual address of the region may differ from the address supplied.) If addr is zero, an address will be selected by the system. The actual starting address of the region is returned. A successful mmap deletes any previous mapping in the allocated address range.
The protections (region accessibility) are specified in the prot argument by OR'ing the following values:
The flags parameter specifies the type of the mapped object, mapping options, and whether modifications made to the mapped copy of the page are private to the process or are to be shared with other references. Sharing, mapping type, and options are specified in the flags argument by OR'ing the following values:
MAP_ANONmust currently be -1 indicating no name is associated with the region.
mmapwill fail. If
MAP_FIXEDis specified, addr must be a multiple of the pagesize. Use of this option is discouraged.
MAP_PRIVATE, modifications made by others are not visible. This option is deprecated, shouldn't be used and behaves just like
MAP_PRIVATEin the current implementation.
The current design does not allow a process to specify the
location of swap space. In the future we may define an additional mapping
MAP_SWAP, in which the file descriptor
argument specifies a file or device to which swapping should be done.
mmapreturns a pointer to the mapped region. Otherwise, a value of
MAP_FAILEDis returned and errno is set to indicate the error. The symbol
MAP_FAILEDis defined in the header ⟨sys/mman.h⟩. No successful return from
mmap() will return the value
mmap() will fail if:
PROT_READwas specified as part of the prot parameter and fd was not open for reading. The flags
PROT_WRITEwere specified as part of the flags and prot parameters and fd was not open for writing.
MAP_FIXEDwas specified and the addr parameter was not page aligned or addr and size specify a region that would extend beyond the end of the address space. fd did not reference a regular or character special file.
MAP_FIXEDwas specified and the addr parameter wasn't available.
MAP_ANONwas specified and insufficient memory was available.
PROT_WRITEwithout also specifying
PROT_READis useless (results in a segmentation fault when first accessing the mapping). This means that such descriptors must be opened with
O_RDWR, which requires both read and write permissions on the underlying object.
|April 11, 2011||OpenBSD-5.1|