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 ALSOlam_rfstate(2), lam_rfrmfd(2)LAM 7.1.2 March, 2006 LAM_RFPOSIX(2)