On Oct 21, 2013, at 10:53 AM, Jesse Becker wrote:
> On Mon, Oct 21, 2013 at 04:30:55PM +0200, devzero@xxxxxx wrote:
>> yes, at least.
>>
>> perhaps i would even think about adding a hint via printk`s in the driver code ("this is a block device probably shared with other nodes, be warned not to use an ordinary filesystem with it"), but i´m not sure if that would get accepted upstream.
>
> If the mounts are read-only, I don't see why you *couldn't* mount it
> to multiple systems. In this case, you could easily use a "normal"
> filesystem. I can think of a few cases where this would be beneficial,
> even. It's the SysAdmin's job to make sure things are handled properly
> so you don't trash you data.
>
> That said, I completly agree with having a note in the Readme file, or
> even a "WARNING_README_FIRST" file.
I have been surprised in the past to observe writes being performed to the block device when the filesystem had been mounted read only. Because not many people do this, and those who do insist that it's safe, I haven't needed to look into the matter more closely.
Regarding the idea for a printk warning, the aoe driver doesn't examine the contents of the data that the Linux block layer wants read or written. I think that a more natural place to generate a warning would be in the individual file systems. A file system like ext3 has the ability to store information to the block device that specifies what host is using the block device exclusively. It would mean patching all the different file systems, though.
I'll make a note to update the README file. Thanks, all, for the input.
--
Ed Cashin
ecashin@xxxxxxxxxx
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