синхронизировать память с физическим хранилищем (synchronize memory with physical storage)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
msync — synchronize memory with physical storage
Синопсис (Synopsis)
#include <sys/mman.h>
int msync(void *addr, size_t len, int flags);
Описание (Description)
The msync() function shall write all modified data to permanent
storage locations, if any, in those whole pages containing any
part of the address space of the process starting at address addr
and continuing for len bytes. If no such storage exists, msync()
need not have any effect. If requested, the msync() function
shall then invalidate cached copies of data.
The implementation may require that addr be a multiple of the
page size as returned by sysconf().
For mappings to files, the msync() function shall ensure that all
write operations are completed as defined for synchronized I/O
data integrity completion. It is unspecified whether the
implementation also writes out other file attributes. When the
msync() function is called on MAP_PRIVATE mappings, any modified
data shall not be written to the underlying object and shall not
cause such data to be made visible to other processes. It is
unspecified whether data in MAP_PRIVATE mappings has any
permanent storage locations. The effect of msync() on a shared
memory object or a typed memory object is unspecified. The
behavior of this function is unspecified if the mapping was not
established by a call to mmap().
The flags argument is constructed from the bitwise-inclusive OR
of one or more of the following flags defined in the <sys/mman.h>
header:
┌──────────────────┬──────────────────────────────┐
│Symbolic Constant │ Description │
├──────────────────┼──────────────────────────────┤
│MS_ASYNC │ Perform asynchronous writes. │
│MS_SYNC │ Perform synchronous writes. │
│MS_INVALIDATE │ Invalidate cached data. │
└──────────────────┴──────────────────────────────┘
When MS_ASYNC is specified, msync() shall return immediately once
all the write operations are initiated or queued for servicing;
when MS_SYNC is specified, msync() shall not return until all
write operations are completed as defined for synchronized I/O
data integrity completion. Either MS_ASYNC or MS_SYNC shall be
specified, but not both.
When MS_INVALIDATE is specified, msync() shall invalidate all
cached copies of mapped data that are inconsistent with the
permanent storage locations such that subsequent references shall
obtain data that was consistent with the permanent storage
locations sometime between the call to msync() and the first
subsequent memory reference to the data.
If msync() causes any write to a file, the file's last data
modification and last file status change timestamps shall be
marked for update.
Возвращаемое значение (Return value)
Upon successful completion, msync() shall return 0; otherwise, it
shall return -1 and set errno to indicate the error.
Ошибки (Error)
The msync() function shall fail if:
EBUSY Some or all of the addresses in the range starting at addr
and continuing for len bytes are locked, and MS_INVALIDATE
is specified.
EINVAL The value of flags is invalid.
ENOMEM The addresses in the range starting at addr and continuing
for len bytes are outside the range allowed for the
address space of a process or specify one or more pages
that are not mapped.
The msync() function may fail if:
EINVAL The value of addr is not a multiple of the page size as
returned by sysconf().
The following sections are informative.
Примеры (Examples)
None.
Использование в приложениях (Application usage)
The msync() function is only supported if the Synchronized Input
and Output option is supported, and thus need not be available on
all implementations.
The msync() function should be used by programs that require a
memory object to be in a known state; for example, in building
transaction facilities.
Normal system activity can cause pages to be written to disk.
Therefore, there are no guarantees that msync() is the only
control over when pages are or are not written to disk.
Обоснование (Rationale)
The msync() function writes out data in a mapped region to the
permanent storage for the underlying object. The call to msync()
ensures data integrity of the file.
After the data is written out, any cached data may be invalidated
if the MS_INVALIDATE flag was specified. This is useful on
systems that do not support read/write consistency.
Будущие направления (Future directions)
None.
Смотри также (See also)
mmap(3p), sysconf(3p)
The Base Definitions volume of POSIX.1‐2017, sys_mman.h(0p)
