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NAMEremap_file_pages - create a nonlinear file mapping
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <sys/mman.h> int remap_file_pages(void *addr, size_t size, int prot, size_t pgoff, int flags);
DESCRIPTIONNote: this system call is (since Linux 3.16) deprecated and will eventually be replaced by a slower in-kernel emulation. Those few applications that use this system call should consider migrating to alternatives.
The remap_file_pages() system call is used to create a nonlinear mapping, that is, a mapping in which the pages of the file are mapped into a nonsequential order in memory. The advantage of using remap_file_pages() over using repeated calls to mmap(2) is that the former approach does not require the kernel to create additional VMA (Virtual Memory Area) data structures.
To create a nonlinear mapping we perform the following steps:
- Use mmap(2) to create a mapping (which is initially linear). This mapping must be created with the MAP_SHARED flag.
- Use one or more calls to remap_file_pages() to rearrange the correspondence between the pages of the mapping and the pages of the file. It is possible to map the same page of a file into multiple locations within the mapped region.
arguments specify the region of the file that is to be relocated
within the mapping:
is a file offset in units of the system page size;
is the length of the region in bytes.
The addr argument serves two purposes. First, it identifies the mapping whose pages we want to rearrange. Thus, addr must be an address that falls within a region previously mapped by a call to mmap(2). Second, addr specifies the address at which the file pages identified by pgoff and size will be placed.
The values specified in addr and size should be multiples of the system page size. If they are not, then the kernel rounds both values down to the nearest multiple of the page size.
The prot argument must be specified as 0.
The flags argument has the same meaning as for mmap(2), but all flags other than MAP_NONBLOCK are ignored.
RETURN VALUEOn success, remap_file_pages() returns 0. On error, -1 is returned, and errno is set appropriately.
- addr does not refer to a valid mapping created with the MAP_SHARED flag.
- addr, size, prot, or pgoff is invalid.