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download PDF document: posix_fadvise.2.pdf

POSIX_FADVISE(2) FreeBSD System Calls Manual POSIX_FADVISE(2)
NAME posix_fadvise - give advice about use of file data
LIBRARY Standard C Library (libc, -lc)
SYNOPSIS #include <fcntl.h>
int posix_fadvise(int fd, off_t offset, off_t len, int advice);
DESCRIPTION The posix_fadvise() system call allows a process to describe to the system its data access behavior for an open file descriptor fd. The advice covers the data starting at offset offset and continuing for len bytes. If len is zero, all data from offset to the end of the file is covered.
The behavior is specified by the advice parameter and may be one of:
POSIX_FADV_NORMAL Tells the system to revert to the default data access behavior.
POSIX_FADV_RANDOM Is a hint that file data will be accessed randomly, and prefetching is likely not advantageous.
POSIX_FADV_SEQUENTIAL Tells the system that file data will be accessed sequentially. This currently does nothing as the default behavior uses heuristics to detect sequential behavior.
POSIX_FADV_WILLNEED Tells the system that the specified data will be accessed in the near future. The system may initiate an asynchronous read of the data if it is not already present in memory.
POSIX_FADV_DONTNEED Tells the system that the specified data will not be accessed in the near future. The system may decrease the in-memory priority of clean data within the specified range and future access to this data may require a read operation.
POSIX_FADV_NOREUSE Tells the system that the specified data will only be accessed once and then not reused. The system may decrease the in-memory priority of data once it has been read or written. Future access to this data may require a read operation.
RETURN VALUES If successful, posix_fadvise() returns zero. It returns an error on failure, without setting errno.
ERRORS Possible failure conditions:
[ENODEV] The fd argument does not refer to a regular file.
[ESPIPE] The fd argument is associated with a pipe or FIFO.
[EIO] An I/O error occurred while reading from or writing to a file system.
[EINTEGRITY] Corrupted data was detected while reading from the file system.
SEE ALSO madvise(2)
STANDARDS The posix_fadvise() interface conforms to IEEE Std 1003.1-2001 ("POSIX.1").
HISTORY The posix_fadvise() system call first appeared in FreeBSD 9.1.
FreeBSD 14.0-RELEASE-p11 March 30, 2020 FreeBSD 14.0-RELEASE-p11