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NAMEreadahead - initiate file readahead into page cache
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h> ssize_t readahead(int fd, off64_t offset, size_t count);
DESCRIPTIONreadahead() initiates readahead on a file so that subsequent reads from that file will be satisfied from the cache, and not block on disk I/O (assuming the readahead was initiated early enough and that other activity on the system did not in the meantime flush pages from the cache).
The fd argument is a file descriptor identifying the file which is to be read. The offset argument specifies the starting point from which data is to be read and count specifies the number of bytes to be read. I/O is performed in whole pages, so that offset is effectively rounded down to a page boundary and bytes are read up to the next page boundary greater than or equal to (offset+count). readahead() does not read beyond the end of the file. The current file offset of the open file referred to by fd is left unchanged.
RETURN VALUEOn success, readahead() returns 0; on failure, -1 is returned, with errno set to indicate the cause of the error.
- fd is not a valid file descriptor or is not open for reading.
- fd does not refer to a file type to which readahead() can be applied.