linux-ext4 - Re: blkid oddities with stale devices in the cache

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Message-ID: <48704BB9.1090501@redhat.com>
Date:	Sat, 05 Jul 2008 23:36:09 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
CC:	Theodore Tso <tytso@....edu>
Subject: Re: blkid oddities with stale devices in the cache

Eric Sandeen wrote:
> This is w.r.t. https://bugzilla.redhat.com/show_bug.cgi?id=452333
> 
> Dave had a few stale entries in blkid.tab; label from a usb key showed
> up under several non-existent, stale device names.  fstab had LABEL=,
> mounting by label failed because blkid returned a stale, nonexistent device.

Ted, ping (when you're done kernel-wrangling anyway)?  Any thoughts on
this?  Returning cached data for a device when stat says ENOENT seems
very weird (and wrong).

Thanks,

-Eric

> It seems there's a problem in blkid_verify():
> 
>         if (((probe.fd = open(dev->bid_name, O_RDONLY)) < 0) ||
>             (fstat(probe.fd, &st) < 0)) {
>                 if (probe.fd >= 0) close(probe.fd);
>                 if ((errno != EPERM) && (errno != EACCES) &&
>                     (errno != ENOENT)) {
>                         DBG(DEBUG_PROBE,
>                             printf("blkid_verify: error %s (%d) while "
>                                    "opening %s\n", strerror(errno), errno,
>                                    dev->bid_name));
>                         blkid_free_dev(dev);
>                         return NULL;
>                 }
>                 /* We don't have read permission, just return cache data. */
>                 DBG(DEBUG_PROBE,
>                     printf("returning unverified data for %s\n",
>                            dev->bid_name));
>                 return dev;
> 
> We find the bad/stale device in the cache, and stat it - if the device
> doesn't exist, we get ENOENT.  But we return the stale data for the
> nonexistent device anyway.  Eh?
> 
> http://git.kernel.org/?p=fs/ext2/e2fsprogs.git;a=commitdiff;h=8bcaaabb1a023af4852dbf0dba76249982c62e40
> 
> did this:
> 
> When a nonprivileged user uses the blkid command, we want to keep the
> cached filesystem information, and opening a device file could result
> in an EACCESS or ENOENT (if an intervening directory is mode 700).  We
> were previously testing for EPERM, which was really the wrong error
> code to be testing against.
> 
> But do we really want to do this in the case of ENOENT?  It seems like
> this is going to grow a crop of missing devices in the cache, no?
> 
> Thanks,
> 
> -Eric
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