exchangedata(2) [mojave man page]

EXCHANGEDATA(2) 					      BSD System Calls Manual						   EXCHANGEDATA(2)

NAME

     exchangedata -- atomically exchange data between two files

SYNOPSIS

     #include <unistd.h>
     #include <sys/attr.h>

     int
     exchangedata(const char * path1, const char * path2, unsigned int options);

DESCRIPTION

     The exchangedata() function swaps the contents of the files referenced by path1 and path2 in an atomic fashion.  That is, all concurrent pro-
     cesses will either see the pre-exchanged state or the post-exchanged state; they can never see the files in an inconsistent state.  The data
     in all forks is swapped in this way.  The options parameter lets you control specific aspects of the function's behaviour.

     Open file descriptors follow the swapped data.  Thus, a descriptor that previously referenced path1 will now reference the data that's acces-
     sible via path2, and vice versa.

     In general, the file attributes (metadata) are not exchanged.  Specifically, the object identifier attributes (that is, the ATTR_CMN_OBJID
     and ATTR_CMN_OBJPERMANENTID attributes as defined by the getattrlist(2) function) are not swapped.  An exception to this general rule is that
     the modification time attribute ( ATTR_CMN_MODTIME ) is swapped.

     When combined, these features allow you to implement a 'safe save' function that does not break references to the file (for example,
     aliases).	You first save the new contents to a temporary file and then exchange the data of the original file and the temporary.	Programs
     that reference the file via an object identifier will continue to reference the original file, but now it has the new data.

     The path1 and path2 parameters must both reference valid files.  All directories listed in the path names leading to these files must be
     searchable.  You must have write access to the files.

     The options parameter is a bit set that controls the behaviour of exchangedata().	The following option bits are defined.

     FSOPT_NOFOLLOW  If this bit is set, exchangedata() will not follow a symlink if it occurs as the last component of path1 or path2.

RETURN VALUES

     Upon successful completion a value of 0 is returned.  Otherwise, a value of -1 is returned and errno is set to indicate the error.

COMPATIBILITY

     Not all volumes support exchangedata().  You can test whether a volume supports exchangedata() by using getattrlist(2) to get the volume
     capabilities attribute ATTR_VOL_CAPABILITIES, and then testing the VOL_CAP_INT_EXCHANGEDATA flag.

ERRORS

     exchangedata() will fail if:

     [ENOTSUP]		The volume does not support exchangedata().

     [ENOTDIR]		A component of the path prefix is not a directory.

     [ENAMETOOLONG]	A component of a path name exceeded NAME_MAX characters, or an entire path name exceeded PATH_MAX characters.

     [ENOENT]		Either file does not exist.

     [EACCES]		Search permission is denied for a component of the path prefix.

     [ELOOP]		Too many symbolic links were encountered in translating the pathname.

     [EFAULT]		path1 or path2 points to an invalid address.

     [EXDEV]		path1 and path2 are on different volumes (mounted file systems).

     [EINVAL]		path1 or path2 reference the same file.

     [EINVAL]		You try to exchange something other than a regular file (for example, a directory).

     [EIO]		An I/O error occurred while reading from or writing to the file system.

SEE ALSO

     getattrlist(2), rename(2)

HISTORY

     A exchangedata() function call appeared in Darwin 1.3.1 (Mac OS X version 10.0).  It was deprecated in macOS 10.13.

Darwin								 December 15, 2003							    Darwin

Check Out this Related Man Page

link(2) 							System Calls Manual							   link(2)

NAME

       link() - link to a file

SYNOPSIS

DESCRIPTION

       The  system  call  creates a new link (directory entry) for the existing file.  path1 points to a path name naming an existing file.  path2
       points to a path name naming the new directory entry to be created.

RETURN VALUE

       Upon successful completion, returns zero.  Otherwise, it returns -1 and sets (see errno(2)) to indicate the error.

ERRORS

       The system call fails and no link is created if one or more of the following is true:

	      A component of either path prefix denies search permission.

	      The requested link requires writing in a directory
			     that does not permit writing.

	      The user's or group's disk quota block limit has been reached for this file system.

	      The link named by
			     path2 exists.

	      path	     points outside the allocated address space of the process.  The reliable detection of this  error	is  implementation
			     dependent.

	      Too many symbolic links were encountered in translating either path name.

	      The maximum number of links to a file would be exceeded.

	      Either the specified path exceeds
			     bytes, or a component of either specified path exceeds while is in effect.

	      The file named by
			     path1 does not exist.

	      A component of either path prefix does not exist.

	      path2	     points to a null path name.

	      path1	     or path2 is null.

	      The directory to contain the file cannot be extended.

	      A component of either path prefix is not a directory.

	      The file named by
			     path1  is	a  directory  and  the	effective user ID is not a user who has appropriate privileges.  Some file systems
			     return this error whenever path1 names a directory, regardless of the user ID.

	      The requested link requires writing in a directory
			     on a read-only file system.

	      The link named by
			     path2 and the file named by path1 are on different logical devices (file systems).

SEE ALSO

       cp(1), link(1M), symlink(2), unlink(2), symlink(4), privileges(5).

STANDARDS CONFORMANCE

																	   link(2)

Linux and UNIX Man Pages

exchangedata(2) [mojave man page]

Check Out this Related Man Page