posix_fallocate - allocate file space


#define _XOPEN_SOURCE 600 #include <fcntl.h>

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


The function posix_fallocate() ensures that disk space is allocated for the file referred to by the descriptor fd for the bytes in the range starting at offset and continuing for len bytes. After a successful call to posix_fallocate(), subsequent writes to bytes in the specified range are guaranteed not to fail because of lack of disk space.

If the size of the file is less than offset+len, then the file is increased to this size; otherwise the file size is left unchanged.


posix_fallocate() returns zero on success, or an error number on failure. Note that errno is not set.


EBADF fd is not a valid file descriptor, or is not opened for writing.
EFBIG offset+len exceeds the maximum file size.
EINVAL offset was less than 0, or len was less than or equal to 0.
ENODEV fd does not refer to a regular file.
ENOSPC There is not enough space left on the device containing the file referred to by fd.
ESPIPE fd refers to a pipe of file descriptor.


posix_fallocate() is available since glibc 2.1.94.



POSIX.1-2008 says that an implementation shall give the EINVAL error if len was 0, or offset was less than 0. POSIX.1-2001 says that an implementation shall give the EINVAL error if len is less than 0, or offset was less than 0, and may give the error if len equals zero.


fallocate(2), lseek(2), posix_fadvise(2), feature_test_macros(7)


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