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unix file system V filename limit

 
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Old 03-16-2008
The filenames are stored in the directory. A directory is a table with a name and an inode number. The directory called "etc" in the "/" filesystem might have an entry like (passwd,3115) and this means that the file called "passwd" is inode 3115, so we can read inode 31115 to get /etc/passwd. The directory does indeed consume space. That's why I said that "space allocated to filenames is not available for file data". If you create a directory and put 10,000 files in it, you will have a large directory and that directory does indeed consume space that otherwise could have been used for file data.

With the original unix file system, directory enties were fixed in size. 14 bytes is all that was allocated to names. This made changing your mind later very hard, but it could have been just as easily designed with a different fixed size. These days just about everyone has variable sized directory entries and that include HP-US UFS which is willing to enforce that 14 character limit.
 
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LEARN ABOUT PLAN9

u9fs

U9FS(4) 						     Kernel Interfaces Manual							   U9FS(4)

NAME

       u9fs - serve 9P from Unix

SYNOPSIS

       u9fs [ directory ]

DESCRIPTION

       U9fs  is not a Plan 9 program.  Instead it is a program that serves Unix files to Plan 9 machines using the 9P protocol (see intro(5)).	It
       is to be invoked on a Unix machine by inetd with its standard input, output, and error connected to a network connection, typically TCP	on
       an  Ethernet.   It runs as user root and multiplexes access to multiple Plan 9 clients over the single wire.  It simulates Unix permissions
       itself by assuming Plan 9 uids match Unix login names.

       If a directory is specified u9fs first does a Unix chroot system call to that directory.

       Plan 9 calls this service 9fs with TCP service number 564 on the Ethernet.  Set up this way on a machine called, say, kremvax, u9fs may	be
       connected to the name space of a Plan 9 process by

	      9fs kremvax

       Due  to	a bug in some versions of the IP software, some systems will not accept the service name 9fs, thinking it a service number because
       of the initial digit.  If so, run the service as u9fs or 564 and do the srv and mount by hand:

	      srv tcp!kremvax!u9fs
	      mount -c /srv/tcp!kremvax!u9fs /n/kremvax

       For more information on this procedure, see srv(4) and bind(1).

       U9fs serves the entire file system of the Unix machine.	It forbids access to devices because the program is single-threaded and may  block
       unpredictably.	Using  the attach specifier device connects to a file system identical to the usual system except it permits device access
       (and may block unpredictably):

	      srv tcp!kremvax!9fs
	      mount -c /srv/tcp!kremvax!9fs /n/kremvax device

       (The 9fs command does not accept an attach specifier.)  Even so, device access may produce unpredictable results if the block size  of  the
       device is greater than 8192, the maximum data size of a 9P message.

       The  source to u9fs is in the Plan 9 directory /sys/src/cmd/unix/u9fs.  To install u9fs on a Unix system, copy the source to a directory on
       that system.  Edit the makefile to set LOG to a proper place for a log file and to set the compile-time configuration correctly.  Then com-
       pile with an ANSI C compiler and install in /usr/etc/u9fs.  Install this line in inetd.conf:

	      9fs     stream  tcp     nowait  root   /usr/etc/u9fs   u9fs

       and this in services:

	      9fs     564/tcp	    9fs  # Plan 9 fs

SOURCE

       /sys/src/cmd/unix/u9fs

DIAGNOSTICS

       Problems are reported to /tmp/u9fs.log.	A compile-time flag enables chatty debugging.

SEE ALSO

       bind(1), srv(4), ip(3), nfsserver(8)

BUGS

       The implementation of devices is unsatisfactory.

																	   U9FS(4)