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LAM_RFPOSIX(2)		      LAM REMOTE LIBRARY		LAM_RFPOSIX(2)

NAME
       lam_rfposix - LAM POSIX-like remote file service

DESCRIPTION
       The  remote  file  daemon,  filed,  provides  POSIX file access for any
       client process in the LAM multicomputer.	 Some services	are  LAM  spe‐
       cific  (see  lam_rfrmfd(2))).  Most of services mirror local POSIX ser‐
       vices and these are listed below.

	      open(2)	     open file
	      close(2)	     close file descriptor
	      read(2)	     read input
	      write(2)	     write output
	      lseek(2)	     set or increment position in file
	      access(2)	     check permissions and/or existance of a file
	      mkdir(2)	     create a directory
	      chdir(2)	     change current working directory
	      fstat(2)	     get status on a file descriptor
	      stat(2)	     get status on a file name
	      dup(2)	     duplicate a file descriptor
	      dup2(2)	     duplicate a file descriptor to a specific handle
	      system(3)	     issue a command to sh(1)
	      rmdir(2)	     remove a directory
	      unlink(2)	     remove a file
	      getwd(3)	     get name of current working directory
	      ftruncate(2)   set open file to specified length
	      truncate(2)    set named file to specified length

       The names of the LAM versions of these  functions  are  prepended  with
       'lam_rf', for example lam_rfopen(), lam_rfclose(), etc.	The parameters
       are the same as in the  POSIX  calls.   Special	flag  bits  passed  to
       lam_rfopen(2)  will  invoke  special  LAM  functionality.  These flags,
       defined in <freq.h>, are listed below.

	      LAM_O_LOCK     lock a file permanently active
	      LAM_O_REUSE    reuse existing open descriptor with same file name
	      LAM_O_1WAY     do not reply to write requests
	      LAM_O_DINT4    data are four-byte integers
	      LAM_O_DFLT4    data are four-byte reals (single precision)
	      LAM_O_DFLT8    data are eight-byte reals (double precision)

       By default, files are accessed on the origin node.  The node  ID	 of  a
       file  can be specified by prepending the file name with the node ID and
       a `:'.  The example below opens the file "foo" on node 15.

		   lam_rfopen("15:foo", O_RDWR, 0);

       An active LAM  file  descriptor	has  an	 associated  open  POSIX  file
       descriptor.   Since  the	 daemon	 can maintain only a limited number of
       open POSIX files, it periodically has to close them and reopen them for
       a  different  LAM  file	descriptor.   The  global  number  of LAM file
       descriptors is unlimited, as are the clients of the  remote  file  ser‐
       vice.   Thus,  performance  problems (like thrashing) may be avoided by
       locking certain files in an active state.  Locked LAM file  descriptors
       will  maintain their open POSIX descriptors until closed by the client.
       Do not overuse this facility.

       Most of the POSIX-like services behave exactly as in  POSIX  (in	 fact,
       the   genuine   article	 is  eventually	 called).   The	 exception  is
       lam_rfwrite() when the data size is greater than the LAM	 network  mes‐
       sage  size  (as	defined	 in <net.h>).  Such requests have to be packe‐
       tized.  The daemon treats each packet as an individual write request in
       order  to remain simple and stateless.  Therefore, long writes on asyn‐
       chronous descriptors are not atomic.

BUGS
       The daemon does not allow read access to	 any  filename	starting  with
       "/dev/".	  This is done to prevent the possibility of the daemon block‐
       ing on a slow device, such as a tty.  This limitation will  be  removed
       in the future.

SEE ALSO
       lam_rfstate(2), lam_rfrmfd(2)

LAM 7.1.2			  March, 2006			LAM_RFPOSIX(2)
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