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>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: David Steele <david@pgmasters.net>
Cc: Bossart, Nathan <bossartn@amazon.com>
Cc: Thomas Munro <thomas.munro@gmail.com>
Subject: Re: pg11+: pg_ls_*dir LIMIT 1: temporary files .. not closed at end-of-transaction
Date: Sun, 29 Mar 2020 12:37:05 -0400
Message-ID: <27064.1585499825@sss.pgh.pa.us> (raw)
In-Reply-To: <28906.1585422475@sss.pgh.pa.us>
References: <27334.1583692669@sss.pgh.pa.us>
<20200308191456.GD1357@telsasoft.com>
<5679.1583696409@sss.pgh.pa.us>
<20200311111921.GQ29065@telsasoft.com>
<21724.1583955158@sss.pgh.pa.us>
<20200312121156.GB29065@telsasoft.com>
<20200316155306.GM26184@telsasoft.com>
<3061.1584409130@sss.pgh.pa.us>
<20200317020017.GT26184@telsasoft.com>
<24244.1585415634@sss.pgh.pa.us>
<20200328183904.GI20103@telsasoft.com>
<28906.1585422475@sss.pgh.pa.us>
I wrote:
> Justin Pryzby <pryzby@telsasoft.com> writes:
>> 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.)
After looking at the callers of pg_ls_dir_files, and noticing that
it's already defined to ignore anything that's not a regular file,
I think switching to lstat makes sense.
I also grepped the other uses of ReadDir[Extended], and didn't see
any other ones that seemed desperately in need of changing.
So the attached seems like a sufficient fix.
regards, tom lane
Attachments:
[text/x-diff] ignore-concurrent-removals-in-pg_ls_dir_files.patch (731B, ../27064.1585499825@sss.pgh.pa.us/2-ignore-concurrent-removals-in-pg_ls_dir_files.patch)
download | inline diff:diff --git a/src/backend/utils/adt/genfile.c b/src/backend/utils/adt/genfile.cindex 01185f2..8429a12 100644--- a/src/backend/utils/adt/genfile.c+++ b/src/backend/utils/adt/genfile.c@@ -596,10 +596,15 @@ pg_ls_dir_files(FunctionCallInfo fcinfo, const char *dir, bool missing_ok)
/* Get the file info */
snprintf(path, sizeof(path), "%s/%s", dir, de->d_name);
- if (stat(path, &attrib) < 0)+ if (lstat(path, &attrib) < 0)+ {+ /* Ignore concurrently-deleted files, else complain */+ if (errno == ENOENT)+ continue;
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not stat file \"%s\": %m", path)));
+ }
/* Ignore anything but regular files */
if (!S_ISREG(attrib.st_mode))
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, pryzby@telsasoft.com, coelho@cri.ensmp.fr, alvherre@2ndquadrant.com, david@pgmasters.net, bossartn@amazon.com, thomas.munro@gmail.com
Subject: Re: pg11+: pg_ls_*dir LIMIT 1: temporary files .. not closed at end-of-transaction
In-Reply-To: <27064.1585499825@sss.pgh.pa.us>
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