Following is the modified version of the manpage originally submitted by David Chinner. Please use `nroff -man fallocate.2 | less` to view. .TH fallocate 2 .SH NAME fallocate \- allocate or remove file space .SH SYNOPSIS .nf .B #include <sys/syscall.h> .PP .BI "int syscall(int, int fd, int mode, loff_t offset, loff_t len); .Op .SH DESCRIPTION The .BR fallocate syscall allows a user to directly manipulate the allocated disk space for the file referred to by .I fd for the byte range starting at .IR offset and continuing for .IR len bytes. The .I mode parameter determines the operation to be performed on the given range. Currently there are four modes: .TP .B FALLOC_ALLOCATE allocates and initialises to zero the disk space within the given range. After a successful call, subsequent writes are guaranteed not to fail because of lack of disk space. If the size of the file is less than .IR offset + len , then the file is increased to this size; otherwise the file size is left unchanged. .B FALLOC_ALLOCATE closely resembles .B posix_fallocate(3) and is intended as a method of optimally implementing this function. .B FALLOC_ALLOCATE may allocate a larger range that was specified. .TP .B FALLOC_RESV_SPACE provides the same functionality as .B FALLOC_ALLOCATE except it does not ever change the file size. This allows allocation of zero blocks beyond the end of file and is useful for optimising append workloads. .TP .B FALLOC_DEALLOCATE removes any preallocated space within the given range. The file size may change if deallocation is towards the end of the file. .TP .B FALLOC_UNRESV_SPACE removes the underlying disk space within the given range. The disk space shall be removed regardless of it's contents so both allocated space from .B FALLOC_ALLOCATE and .B FALLOC_RESV_SPACE as well as from .B write(3) will be removed. .B FALLOC_UNRESV_SPACE shall never remove disk blocks outside the range specified. .B FALLOC_UNRESV_SPACE shall never change the file size. If changing the file size is required when deallocating blocks from an offset to end of file (or beyond end of file) is required, .B ftuncate64(3) or .B FALLOC_DEALLOCATE should be used. .SH "RETURN VALUE" .BR fallocate() returns zero on success, or an error number on failure. Note that .IR errno is not set. .SH "ERRORS" .TP .B EBADF .I fd is not a valid file descriptor, or is not opened for writing. .TP .B EFBIG .I offset+len exceeds the maximum file size. .TP .B EINVAL .I offset or .I len was less than 0. .TP .B ENODEV .I fd does not refer to a regular file or a directory. .TP .B ENOSPC There is not enough space left on the device containing the file referred to by .IR fd. .TP .B ESPIPE .I fd refers to a pipe of file descriptor. .B ENOSYS The filesystem underlying the file descriptor does not support this operation. .SH AVAILABILITY The .BR fallocate () system call is available since 2.6.XX .SH "SEE ALSO" .BR syscall (2), .BR posix_fadvise (3) .BR ftruncate (3) - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
