Can I close FD after mmap?
After the mmap() call has returned, the file descriptor, fd, can be closed immediately without invalidating the mapping. The prot argument describes the desired memory protection of the mapping (and must not conflict with the open mode of the file).
Why mmap is fast?
Using wide vector instructions for data copying effectively utilizes the memory bandwidth, and combined with CPU pre-fetching makes mmap really really fast.
Can mmap fail?
The mmap() function shall fail if: EACCES. The fildes argument is not open for read, regardless of the protection specified, or fildes is not open for write and PROT_WRITE was specified for a MAP_SHARED type mapping.
What is mmap offset?
The mmap() function asks to map ‘length’ bytes starting at offset ‘offset’ from the file (or other object) specified by the file descriptor fd into memory, preferably at address ‘start’. Sepcifically, for the last argument: ‘offset’ should be a multiple of the page size as returned by getpagesize(2).
Is the mmap call visible to other processes?
Updates to the mapping are not visible to other processes mapping the same file, and are not carried through to the underlying file. It is unspecified whether changes made to the file after the mmap () call are visible in the mapped region. Both MAP_SHARED and MAP_PRIVATE are described in POSIX.1-2001 and POSIX.1-2008.
Do you need FD for MAP _ ANONYMOUS in mmap?
MAP_ANONYMOUS The mapping is not backed by any file; its contents are initialized to zero. The fd argument is ignored; however, some implementations require fd to be -1 if MAP_ANONYMOUS (or MAP_ANON) is specified, and portable applications should ensure this.
What is the length argument for mmap in ADDR?
mmap () creates a new mapping in the virtual address space of the calling process. The starting address for the new mapping is specified in addr. The length argument specifies the length of the mapping (which must be greater than 0).