MPAGE_WRITEPAGES(9) The Linux VFS MPAGE_WRITEPAGES(9)NAME
mpage_writepages - walk the list of dirty pages of the given address space & writepage all of them
SYNOPSIS
int mpage_writepages(struct address_space * mapping, struct writeback_control * wbc, get_block_t get_block);
ARGUMENTS
mapping
address space structure to write
wbc
subtract the number of written pages from *wbc->nr_to_write
get_block
the filesystem's block mapper function. If this is NULL then use a_ops->writepage. Otherwise, go direct-to-BIO.
DESCRIPTION
This is a library function, which implements the writepages address_space_operation.
If a page is already under I/O, generic_writepages skips it, even if it's dirty. This is desirable behaviour for memory-cleaning writeback,
but it is INCORRECT for data-integrity system calls such as fsync. fsync and msync need to guarantee that all the data which was dirty at
the time the call was made get new I/O started against them. If wbc->sync_mode is WB_SYNC_ALL then we were called for data integrity and we
must wait for existing IO to complete.
COPYRIGHT Kernel Hackers Manual 2.6. July 2010 MPAGE_WRITEPAGES(9)
Check Out this Related Man Page
SYNC_FILE_RANGE(2) Linux Programmer's Manual SYNC_FILE_RANGE(2)NAME
sync_file_range - sync a file segment with disk
SYNOPSIS
#define _GNU_SOURCE
#include <fcntl.h>
int sync_file_range(int fd, off64_t offset, off64_t nbytes,
unsigned int flags);
DESCRIPTION
sync_file_range() 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:
SYNC_FILE_RANGE_WAIT_BEFORE
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.
SYNC_FILE_RANGE_WRITE
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.
SYNC_FILE_RANGE_WAIT_AFTER
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 portable programs. None of these operations writes out the file's meta-
data. Therefore, unless the application is strictly performing overwrites of already-instantiated disk blocks, there are no guarantees
that the data will be available after a crash. There is no user interface to know if a write is purely an overwrite. On file systems
using copy-on-write semantics (e.g., btrfs) an overwrite of existing allocated 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 systems with volatile disk write caches.
Some details
SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will detect any I/O errors or ENOSPC conditions and will return these to the
caller.
Useful combinations of the flags bits are:
SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE
Ensures that all pages in the specified range which were dirty when sync_file_range() was called are placed under write-out. This
is a start-write-for-data-integrity operation.
SYNC_FILE_RANGE_WRITE
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.
SYNC_FILE_RANGE_WAIT_BEFORE (or SYNC_FILE_RANGE_WAIT_AFTER)
Wait for completion of write-out of all pages in the specified range. This can be used after an earlier SYNC_FILE_RANGE_WAIT_BEFORE
| SYNC_FILE_RANGE_WRITE operation to wait for completion of that operation, and obtain its result.
SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE | SYNC_FILE_RANGE_WAIT_AFTER
This is a write-for-data-integrity operation that will ensure that all pages in the specified range which were dirty when
sync_file_range() was called are committed to disk.
RETURN VALUE
On success, sync_file_range() 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
sync_file_range() appeared on Linux in kernel 2.6.17.
CONFORMING TO
This system call is Linux-specific, and should be avoided in portable programs.
SEE ALSO fdatasync(2), fsync(2), msync(2), sync(2), feature_test_macros(7)COLOPHON
This page is part of release 3.27 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 2010-01-17 SYNC_FILE_RANGE(2)