posix_fallocate - file space control (ADVANCED REALTIME)
The posix_fallocate() function shall ensure that any required storage for regular file data starting at offset and continuing for len bytes is allocated on the file system storage media. If posix_fallocate() returns successfully, subsequent writes to the specified file data shall not fail due to the lack of free space on the file system storage media.
If the offset+ len is beyond the current file size, then posix_fallocate() shall adjust the file size to offset+ len. Otherwise, the file size shall not be changed.
It is implementation-defined whether a previous posix_fadvise() call influences allocation strategy.
Space allocated via posix_fallocate() shall be freed by a successful call to creat() or open() that truncates the size of the file. Space allocated via posix_fallocate() may be freed by a successful call to ftruncate() that reduces the file size to a size smaller than offset+ len.
Upon successful completion, posix_fallocate() shall return zero; otherwise, an error number shall be returned to indicate the error.
The posix_fallocate() function shall fail if:
- The fd argument is not a valid file descriptor.
- The fd argument references a file that was opened without write permission.
- The value of offset+ len is greater than the maximum file size.
- A signal was caught during execution.
- The len argument was zero or the offset argument was less than zero.
- An I/O error occurred while reading from or writing to a file system.
- The fd argument does not refer to a regular file.
- There is insufficient free space remaining on the file system storage media.
- The fd argument is associated with a pipe or FIFO.
The posix_fallocate() function is part of the Advisory Information option and need not be provided on all implementations.
creat(), ftruncate(), open(), unlink(), the Base Definitions volume of IEEE Std 1003.1-2001, <fcntl.h>
First released in Issue 6. Derived from IEEE Std 1003.1d-1999.
In the SYNOPSIS, the inclusion of <sys/types.h> is no longer required.
IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/69 is applied, changing the function prototype in the SYNOPSIS section. The previous prototype was not large file-aware, and the standard developers felt it acceptable to make this change before implementations of this function become widespread.