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NAMEposix_fadvise - give advice about use of file data
SYNOPSISIn fcntl.h Ft int Fn posix_fadvise int fd off_t offset off_t len int advice
DESCRIPTIONThe 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:
- Tells the system to revert to the default data access behavior.
- Is a hint that file data will be accessed randomly, and prefetching is likely not advantageous.
- Tells the system that file data will be accessed sequentially. This currently does nothing as the default behavior uses heuristics to detect sequential behavior.
- 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.
- 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.
- 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 VALUESRv -std posix_fadvise
ERRORSThe 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.