NAME

posix_fallocate — file space control (ADVANCED REALTIME)

SYNOPSIS

[ADV] #include <fcntl.h>

int posix_fallocate(int fd, off_t offset, off_t len);

DESCRIPTION

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.

RETURN VALUE

Upon successful completion, posix_fallocate() shall return zero; otherwise, an error number shall be returned to indicate the error.

ERRORS

The posix_fallocate() function shall fail if:

[EBADF]

The fd argument is not a valid file descriptor.

[EBADF]

The fd argument references a file that was opened without write permission.

[EFBIG]

The value of offset+len is greater than the maximum file size.

[EFBIG]

The value of offset+len exceeds the file size limit of the process. ^[XSI]  A SIGXFSZ signal shall also be generated for the thread.

[EINTR]

A signal was caught during execution.

[EINVAL]

The len argument is less than zero, or the offset argument is less than zero.

[EIO]

An I/O error occurred while reading from or writing to a file system.

[ENODEV]

The fd argument does not refer to a regular file.

[ENOSPC]

There is insufficient free space remaining on the file system storage media.

[ENOTSUP]

The underlying file system does not support this operation.

[ESPIPE]

The fd argument is associated with a pipe or FIFO.

The posix_fallocate() function may fail if:

[EINVAL]

The len argument is zero.

EXAMPLES

None.

APPLICATION USAGE

The posix_fallocate() function is part of the Advisory Information option and need not be provided on all implementations.

Not all file systems are capable of supporting posix_fallocate(), in which case the function will return [ENOTSUP]. However, if a system supports the Advisory Information option, there must be at least one file system that is capable of supporting this function and is available for use in conforming environments. The pathconf() and fpathconf() functions can be used to determine whether a file in a particular file system supports posix_fallocate().

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

creat, ftruncate, open, unlink

XBD <fcntl.h>

CHANGE HISTORY

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.

Issue 7

Austin Group Interpretations 1003.1-2001 #022, #024, and #162 are applied, changing the definition of the [EINVAL] error.

Issue 8

Austin Group Defect 308 is applied, clarifying the handling of [EFBIG] errors.

Austin Group Defect 684 is applied, requiring an [ENOTSUP] error instead of [EINVAL] when the underlying file system does not support posix_fallocate().

Austin Group Defect 687 is applied, changing the APPLICATION USAGE section.

Austin Group Defect 1669 is applied, removing XSI shading from part of the [EFBIG] error relating to the file size limit for the process.