From: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> |
---|---|
To: | Justin Pryzby <pryzby(at)telsasoft(dot)com> |
Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, David Steele <david(at)pgmasters(dot)net>, pgsql-hackers(at)postgresql(dot)org, "Bossart, Nathan" <bossartn(at)amazon(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Subject: | Re: pg_ls_tmpdir to show directories and shared filesets (and pg_ls_*) |
Date: | 2020-03-16 18:21:06 |
Message-ID: | alpine.DEB.2.21.2003161903360.17290@pseudo |
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Thread: | |
Lists: | pgsql-hackers |
Hello Justin,
>> psql> SELECT * FROM pg_ls_dir_recurse('.');
>> ERROR: could not stat file "./base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo/base/foo": Too many levels of symbolic links
>> CONTEXT: SQL function "pg_ls_dir_recurse" statement 1
>>
>> This probably means using lstat instead of (in supplement to?) stat, and
>> probably tell if something is a link, and if so not recurse in them.
>
> Thanks for looking.
>
> I think that opens up a can of worms. I don't want to go into the business of
> re-implementing all of find(1) - I count ~128 flags (most of which take
> arguments). You're referring to find -L vs find -P, and some people would want
> one and some would want another. And don't forget about find -H...
This is not the point. The point is that a link can change a finite tree
into cyclic graph, and you do not want to delve into that, ever.
The "find" command, by default, does not recurse into a link because of
said problem, and the user *must* ask for it and assume the infinite loop
if any.
So if you implement one behavior, it should be not recursing into links.
Franckly, I would not provide the recurse into link alternative, but it
could be implemented if someone wants it, and the problem that come with
it.
> pg_stat_file doesn't expose the file type (I guess because it's not portable?),
You are right that Un*x and Windows are not the same wrt link. It seems
that there is already something about that in port:
"./src/port/dirmod.c:pgwin32_is_junction(const char *path)"
So most of the details are already hidden.
> and I think it's outside the scope of this patch to change that. Maybe it
> suggests that the pg_ls_dir_recurse patch should be excluded.
IMHO, I really think that it should be included. Dealing with links is no
big deal, but you need an additional column in _metadata to tell it is a
link, and there is a ifdef because testing is a little different between
unix and windows. I'd guess around 10-20 lines of code added.
> ISTM if someone wants to recursively list a directory, they should avoid
> putting cycles there, or permission errors, or similar.
Hmmm. I'd say the user should like to be able to call the function and
never have a bad experience with it such as a failure on an infinite loop.
> Or they should write their own C extension that borrows from
> pg_ls_dir_files but handles more arguments.
ISTM that the point of your patch is to provide the basic tool needed to
list directories contents, and handling links somehow is a necessary part
of that.
--
Fabien.
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