linux-ext4 - Re: ext3 read only handling

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Message-ID: <20090127095626.GB18449@elf.ucw.cz>
Date:	Tue, 27 Jan 2009 10:56:26 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	kernel list <linux-kernel@...r.kernel.org>, tytso@....edu,
	jack@...e.cz, sct@...hat.com, akpm@...ux-foundation.org,
	adilger@....com, linux-ext4@...r.kernel.org
Subject: Re: ext3 read only handling

On Thu 2008-09-25 10:15:26, Eric Sandeen wrote:
> Pavel Machek wrote:
> > Inserting read-only ext3 SD card into a machine and trying to mount
> > ext3 volume on it is very unnice :-(.
> > 
> > Is there easy way to "fix" -oro so that it does not write to the
> > media?
> > 
> > (Machine died after I played with that SD card a bit more, but I can't
> > easily reproduce that...)
> 
> Is the block device recognized as readonly?
> 
> ext3_load_journal() does things like:
> 
>         really_read_only = bdev_read_only(sb->s_bdev);
> ...
>                         printk(KERN_INFO "EXT3-fs: INFO: recovery "
>                                         "required on readonly
> filesystem.\n");
>                         if (really_read_only) {
>                                 printk(KERN_ERR "EXT3-fs: write access "
>                                         "unavailable, cannot proceed.\n");
>                                 return -EROFS;
>                         }
> 
> so it shouldn't have tried to replay the log ...
> 
> (replaying the log & writing to the device on a read-only mount is
> another issue, but the behavior today is *supposed* to be such that if
> you cannot write to the device, then even a read-only mount with a dirty
> journal should fail gracefully, not explode ....)

Well, that card is so broken I'm afraid to insert it into machine any
more. I had hard time removing it on last attempt. But these days at
least "ro,noload" is documented, so... 

								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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