posix_fadvise (2)

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(The comments found at the beginning of the groff file "man2/posix_fadvise.2freebsd".)

NAME

posix_fadvise - give advice about use of file data

LIBRARY

Lb libc

SYNOPSIS

In fcntl.h Ft int Fn posix_fadvise int fd off_t offset off_t len int advice

DESCRIPTION

The Fn posix_fadvise system call allows a process to describe to the system its data access behavior for an open file descriptor Fa fd . The advice covers the data starting at offset Fa offset and continuing for Fa len bytes. If Fa len is zero, all data from Fa offset to the end of the file is covered.

The behavior is specified by the Fa 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

Rv -std posix_fadvise

ERRORS

The Fn posix_fadvise system call returns zero on success, and an error on failure:

Bq Er EBADF

The Fa fd argument is not a valid file descriptor.

Bq Er EINVAL

The Fa advice argument is not valid.

Bq Er EINVAL

The Fa offset or Fa len arguments are negative, or Fa offset + Fa len is greater than the maximum file size.

Bq Er ENODEV

The Fa fd argument does not refer to a regular file.

Bq Er ESPIPE

The Fa fd argument is associated with a pipe or FIFO.

SEE ALSO

madvise(2)

STANDARDS

The Fn posix_fadvise interface conforms to St -p1003.1-2001 .

HISTORY

The Fn posix_fadvise system call first appeared in Fx 9.1 .