On my system, given that forward slashes generally work insteadof backward
slashes in Win32 paths, true, and given the current working DRIVE is c: then
the path /cygdrive/c means the same thing in Cygwin and Win32 programs ON MY
SYSTEM,
because I have a directory c:/cygdrive with an NTFS junction c pointing to c:/.
This is a circularity in my file system, and UWin appears to setup a backupcron
job or something, that follows it recursively.
C:\users\Jay>tlist tw1396 tw.exe CWD:
c:\cygdrive\c\cygdrive\c\cygdrive\c\cygdrive\c\c\dev2\cm3.archive\cm3.3\doc\help\gen_html\obliqlibm3\
CmdLine: tw -P -l -F - -G - "-e if ( path ==
'(/afs|/backup|/dev|/proc|/tmp|/usr/tmp|/var/tmp)?(/*)' )
status = SKIP; else if ( type == LNK &&
level < 3 && path ==
'(/home|/usr/local|/usr/common)?(/*)' )
status = FOLLOW; " -d /
What to do?
I can probably at this point abandon this scheme of mine.It did serve a purpose
of not needing to translate paths between Cygwin and Win32.
What is general solution on Unix to avoid following circularities in the file
system forever?I have seen various switches to various utilities for varying
treatment of symbolic links and Ithink even hard links. I realize that hard
links are the same as "no links", except code cannotice a link count > 1 and/or
can notice hitting the same inode number more than once in a walk.
I thought about this some myself in a Win32 context.I had two pieces of code.A
recursive diff and a variant of "du".
For "du", I just changed it to never follow NTFS reparse points, which is what
"junctions" are.
(Backing up a sec: NTFS has always has hard links for files, and not for
directories.Windows 2000 added "reparse points" for directories and files,
which are a general mechanism andthen one application of them is "directory
junctions", which is essentially directory symlinks.)
The reparse points do take a small amount of diskspace for some "metadata" and
do point to somethingthat could take significant space. This interpretation is
not clearly always correct, but for mypurposes ok. That is, a) if you happen
upon the junction target as part of the du walk anyway,its space will count,
just once, which is "correct", assuming you don't care to know what it costs to
replicate to a system that doesn't support junctions b) if you really want
toknow how much space this tree will take to replicate and you DON'T otherwise
hit the target, thenthe result is indeed wrong.I was most interested in the
space taken on the current system, not a replica, and I generallywould hit the
junction target since I ran "du" from "high enough up".
For the recursive diff, I added a manual flag to never follow reparse points.I
really wanted something "automatic" but couldn't come up with one, esp. not a
very small changesince none of the other users had hit this, only me, and the
usage scenarios were broader.
It seems like what you often want is to follow every link/junction, but only at
most once.You also might want to follow zero times. I think limiting the walk
to one ought to be easily coded.Deciding between zero and one I don't think is
automatically decidable.
I have long since concluded that file systems are tremendously more complicated
than mostpeople or code realizes. Probably even more than I realize.
One small tangential example I will give is that of case sensitivity.A lot of
people think they get this: Unix is case sensitive, Windows is not.But it is
much more complicated than that.First of all, it is dependent on the file
system implementation, not so much the "operating system". Either "operating
system" can see either file system implementation, definitely remotely and
pretty much locally too. The "operating systems" are very extensible, via
writing new file system implementations, and have been much extended.Second of
all, you can hop between file system implemenations, such as via symlinks, or
NTFS junctions.
Even on a local Windows system, you can have a FAT volume mounted in an NTFS
directory.
Even what "case insensitivity" means varies, once you start having characters
beyond 7 or 8 bits.
For now I stopped the uwin master service and set it to on-demand start.
I'm not sure I needed anything it was doing.
Later I'll probably remove my circularity. And edit the crontab or whatnot.
I see tw has options for symbolic links.
tw is not necessarily at fault, maybe just the default setup and its use of tw?
Setup finished, but what it left behind is what I mean.
- Jay_______________________________________________
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