Horton

Re: pg11+: pg_ls_*dir LIMIT 1: temporary files .. not closed at end-of-transaction

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: pgsql-hackers@postgresql.org, Fabien COELHO <coelho@cri.ensmp.fr>, Alvaro Herrera <alvherre@2ndquadrant.com>, David Steele <david@pgmasters.net>, "Bossart, Nathan" <bossartn@amazon.com>, Thomas Munro <thomas.munro@gmail.com>
Date: 2020-03-28T19:07:55Z
Lists: pgsql-hackers 
Justin Pryzby <pryzby@telsasoft.com> writes:
> On Sat, Mar 28, 2020 at 01:13:54PM -0400, Tom Lane wrote:
>> so I propose that we fix these directory-scanning functions to silently
>> ignore ENOENT failures from stat().  Are there any for which we should not do
>> that?

> Maybe we should lstat() the file to determine if it's a dangling link; if
> lstat() fails, then skip it.  Currently, we use stat(), which shows metdata of
> a link's *target*.  Maybe we'd change that.

Hm, good point that ENOENT could refer to a symlink's target.  Still,
I'm not sure it's worth going out of our way to disambiguate that,
given that these directories aren't really supposed to contain symlinks.
(And on the third hand, if they aren't supposed to, then maybe these
functions needn't look through any symlinks?  In which case just
substituting lstat for stat would resolve the ambiguity.)

> Note that I have a patch which generalizes pg_ls_dir_files and makes
> pg_ls_dir() a simple wrapper, so if that's pursued, they would behave the same
> unless I add another flag to do otherwise (but behaving the same has its
> merits).  It already uses lstat() to show links to dirs as isdir=no, which was
> needed to avoid recursing into links-to-dirs in the new helper function
> pg_ls_dir_recurse().  https://commitfest.postgresql.org/26/2377/

I think we need a back-patchable fix for the ENOENT failure, seeing that
we back-patched the new regression test; intermittent buildfarm failures
are no fun in any branch.  So new functions aren't too relevant here,
although it's fair to look ahead at whether the same behavior will be
appropriate for them.

			regards, tom lane

Commits

  1. Teach pg_ls_dir_files() to ignore ENOENT failures from stat().

  2. Remove useless pfree()s at the ends of various ValuePerCall SRFs.

  3. Avoid holding a directory FD open across assorted SRF calls.

  4. Document pg_ls_*dir hiding of directories and special files

  5. Avoid holding a directory FD open across pg_ls_dir_files() calls.

  6. Adjust nodeFunctionscan.c to reset transient memory context between calls