31 Dec
2021
31 Dec
'21
9:23 a.m.
In broad strokes, that's exactly what we did in Plan 9, with great results,
as was said here a while back. The paper ended with a plea to do the same
to Unix, which I think is quite doable.
https://9p.io/sys/doc/lexnames.html
-rob
On Fri, Dec 31, 2021 at 2:09 PM Theodore Ts'o <tytso(a)mit.edu> wrote:
On Thu, Dec 30, 2021 at 05:31:09PM -0500, Dan Cross
wrote:
Why? Presumably as you traversed the filesystem, you'd cache, (path
component, inode) pairs and keep a ref on the inode. For any given
file, including $CWD, you'd know it's pathname from the root as you
accessed it, but if it got renamed, it wouldn't matter because you'd
have cached a reference to the inode.
I was responding to Bakul's suggestion that the original Unix
could/should have stored the cwd as a string, instead of a pointer to
a directory inode. If you stored the cwd as a string, then you could
interpret .. by chopping off the last file name component of the
string, and so now you could have hard links to directories and the
file system tree could then be a file system DAG.
I don't think Bakul's proposal would have worked --- although I
suppose if you disallowed directory renames, I guess it could. Noel's
objection above was a performance one, in that if you had to parse the
path every single time, you'd be much more dependent on the namei
cache --- and that PDP-11 didn't have the memory to support a
sufficiently large cache.
- Ted
On Thu, Dec 30, 2021 at 11:41 AM Theodore
Ts'o <tytso(a)mit.edu> wrote:
> On Wed, Dec 29, 2021 at 10:45:12PM -0500, Noel Chiappa wrote:
> > > From: Bakul Shah
> >
> > > My guess is *not* storing a path instead of a ptr to the inode
was done
> > > to save on memory.
> >
> > More probably speed; those old disks were not fast, and on a PDP-11,
disk
> > caches were so small that converting
the path to the current
directory to its
in memory inode could take a bunch of disk reads.
The other problem with storing the path as a string is that if
higher-level directories get renamed, the path would become
invalidated. If you store the cwd as "/foo/bar/baz/quux", and someone
renames "/foo/bar" to "/foo/sadness" the cwd-stored-as-a-string
would
become invalidated.