sync_file_range(2)

1SYNC_FILE_RANGE(2)         Linux Programmer's Manual        SYNC_FILE_RANGE(2)
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NAME

6       sync_file_range - sync a file segment with disk
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SYNOPSIS

9       #define _GNU_SOURCE
10       #include <fcntl.h>
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12       void sync_file_range(int fd, off64_t offset, off64_t nbytes,
13                            unsigned int flags);
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DESCRIPTION

16       sync_file_range() permits fine control when synchronising the open file
17       referred to by the file descriptor fd with disk.
18
19       offset is the starting byte of  the  file  range  to  be  synchronised.
20       nbytes  specifies the length of the range to be synchronised, in bytes;
21       if nbytes is zero, then all bytes from offset through  to  the  end  of
22       file  are synchronised.  Synchronisation is in units of the system page
23       size: offset is rounded down to a page boundary;  (offset+nbytes-1)  is
24       rounded up to a page boundary.
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26       The flags bit-mask argument can include any of the following values:
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28       SYNC_FILE_RANGE_WAIT_BEFORE
29              Wait  upon  write-out  of  all pages in the specified range that
30              have already been submitted to the device driver  for  write-out
31              before performing any write.
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33       SYNC_FILE_RANGE_WRITE
34              Initiate  write-out  of  all  dirty pages in the specified range
35              which are not presently submitted write-out.
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37       SYNC_FILE_RANGE_WAIT_AFTER
38              Wait upon write-out of all pages in the range  after  performing
39              any write.
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41       Specifying flags as 0 is permitted, as a no-op.
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NOTES

44       None  of  these  operations  write out the file's metadata.  Therefore,
45       unless the application is strictly performing  overwrites  of  already-
46       instantiated disk blocks, there are no guarantees that the data will be
47       available after a crash.
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49       SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will  detect
50       any  I/O errors or ENOSPC conditions and will return these to the call‐
51       er.
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53       Useful combinations of the flags bits are:
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55       SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE
56              Ensures that all pages in the specified range which  were  dirty
57              when  sync_file_range()  was  called are placed under write-out.
58              This is a start-write-for-data-integrity operation.
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60       SYNC_FILE_RANGE_WRITE
61              Start write-out of all dirty pages in the specified range  which
62              are  not  presently  under  write-out.   This is an asynchronous
63              flush-to-disk  operation.   This  is  not  suitable   for   data
64              integrity operations.
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66       SYNC_FILE_RANGE_WAIT_BEFORE (or SYNC_FILE_RANGE_WAIT_AFTER)
67              Wait  for  completion of write-out of all pages in the specified
68              range.     This    can    be    used    after     an     earlier
69              SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE operation to
70              wait for completion of that operation, and obtain its result.
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72       SYNC_FILE_RANGE_WAIT_BEFORE       |       SYNC_FILE_RANGE_WRITE       |
73       SYNC_FILE_RANGE_WAIT_AFTER
74              This  is  a  traditional fdatasync(2) operation.  It is a write-
75              for-data-integrity operation that will ensure that all pages  in
76              the  specified range which were dirty when sync_file_range() was
77              called are committed to disk.
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ERRORS

80       EBADF  fd is not a valid file descriptor.
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82       EIO    I/O error.
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84       EINVAL flags specifies an invalid bit; or offset or nbytes is invalid.
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86       ENOMEM Out of memory.
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88       ENOSPC Out of disk space.
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90       ESPIPE fd refers to something  other  than  a  regular  file,  a  block
91              device, a directory, or a symbolic link.
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CONFORMING TO

94       This  system  call is Linux specific, and should be avoided in portable
95       programs.
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VERSIONS

98       sync_file_range() appeared on Linux in kernel 2.6.17.
99