NAME
syncfilerange - sync a file segment with disk SYNOPSIS
#define GNUSOURCE /* See featuretestmacros(7) */
#include
int syncfilerange(int fd, off64t offset, off64t nbytes, unsigned int flags); DESCRIPTION syncfilerange() permits fine control when synchronizing the open file referred to by the file descriptor fd with disk. offset is the starting byte of the file range to be synchronized. nbytes specifies the length of the range to be synchronized, in bytes; if nbytes is zero, then all bytes from offset through to the end of file are synchronized. Synchronization is in units of the system page size: offset is rounded down to a page boundary; (offset+nbytes-1) is rounded up to a page boundary.
The flags bit-mask argument can include any of the following values: SYNCFILERANGEWAITBEFORE
Wait upon write-out of all pages in the specified range that
have already been submitted to the device driver for write-out before performing any write. SYNCFILERANGEWRITE
Initiate write-out of all dirty pages in the specified range
which are not presently submitted write-out. Note that even this may block if you attempt to write more than request queue size. SYNCFILERANGEWAITAFTER
Wait upon write-out of all pages in the range after performing any write.
Specifying flags as 0 is permitted, as a no-op. Warning This system call is extremely dangerous and should not be used in por‐ table programs. None of these operations writes out the file's meta‐ data. Therefore, unless the application is strictly performing over‐
writes of already-instantiated disk blocks, there are no guarantees that the data will be available after a crash. There is no user inter‐ face to know if a write is purely an overwrite. On file systems using
copy-on-write semantics (e.g., btrfs) an overwrite of existing allo‐ cated blocks is impossible. When writing into preallocated space, many file systems also require calls into the block allocator, which this system call does not sync out to disk. This system call does not flush disk write caches and thus does not provide any data integrity on sys‐ tems with volatile disk write caches. Some details SYNCFILERANGEWAITBEFORE and SYNCFILERANGEWAITAFTER will detect any I/O errors or ENOSPC conditions and will return these to the call‐ er. Useful combinations of the flags bits are: SYNCFILERANGEWAITBEFORE | SYNCFILERANGEWRITE Ensures that all pages in the specified range which were dirty
when syncfilerange() was called are placed under write-out.
This is a start-write-for-data-integrity operation. SYNCFILERANGEWRITE
Start write-out of all dirty pages in the specified range which
are not presently under write-out. This is an asynchronous
flush-to-disk operation. This is not suitable for data integrity operations. SYNCFILERANGEWAITBEFORE (or SYNCFILERANGEWAITAFTER)
Wait for completion of write-out of all pages in the specified range. This can be used after an earlier SYNCFILERANGEWAITBEFORE | SYNCFILERANGEWRITE operation to wait for completion of that operation, and obtain its result. SYNCFILERANGEWAITBEFORE | SYNCFILERANGEWRITE | SYNCFILERANGEWAITAFTER
This is a write-for-data-integrity operation that will ensure that all pages in the specified range which were dirty when syncfilerange() was called are committed to disk. RETURN VALUE
On success, syncfilerange() returns 0; on failure -1 is returned and errno is set to indicate the error. ERRORS EBADF fd is not a valid file descriptor. EINVAL flags specifies an invalid bit; or offset or nbytes is invalid. EIO I/O error. ENOMEM Out of memory. ENOSPC Out of disk space. ESPIPE fd refers to something other than a regular file, a block device, a directory, or a symbolic link. VERSIONS syncfilerange() appeared on Linux in kernel 2.6.17. CONFORMING TO
This system call is Linux-specific, and should be avoided in portable programs. NOTES
Some architectures (e.g., PowerPC, ARM) need 64-bit arguments to be aligned in a suitable pair of registers. On such architectures, the call signature of syncfilerange() shown in the SYNOPSIS would force a register to be wasted as padding between the fd and offset arguments. (See syscall(2) for details.) Therefore, these architectures define a different system call that orders the arguments suitably: int syncfilerange2(int fd, unsigned int flags, off64t offset, off64t nbytes); The behavior of this system call is otherwise exactly the same as syncfilerange(). A system call with this signature first appeared on the ARM architec‐ ture in Linux 2.6.20, with the name armsyncfilerange(). It was renamed in Linux 2.6.22, when the analogous system call was added for PowerPC. On architectures where glibc support is provided, glibc transparently wraps syncfilerange2() under the name syncfilerange(). SEE ALSO fdatasync(2), fsync(2), msync(2), sync(2) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2013-04-01 SYNCFILERANGE(2)