[BBLISA] Does read only really mean it?

[Brian O'Neill]

I'm thinking the atime is being updated by the server because the server accessed the file in order to serve it...

Alex Aminoff <alex at basespace.net> wrote:
>On 12/4/2013 10:21 PM, Matt Simmons wrote:
>> My knowledge is somewhat limited to the Linux world, but in my 
>> experience I've never seen a mount be set to 'ro' and have anything 
>> updated. I hate to use the term 'flabbergasted', but I'm pretty sure 
>> that if I saw an implementation that didn't respect the 'ro' flag,
>I'd 
>> be at the very least 'put out', and perhaps even vitriolic.
>>
>Yeah, flabbergasted is a good description of how I felt.
>
>Nevertheless, I tested it and unless I messed up my test, an NFS mount 
>with -o ro, you read a file on the mounted FS, and the access time is 
>updated.
>
>For the test the server was a NetApp, the client was Linux.
>
>There is a mount flag -o noatime that does what I want. But I would 
>argue that this is not right. The simplest behavior - nothing is ever 
>written period - should be what you get by default, and then there
>could 
>be a flag that enables exceptional behavior, that is updating the
>access 
>time.
>
>I can squint and see why it would be the way it is. One perspective is 
>that the naive assumption is that reading off a RO filesystem should be
>
>just like reading any other way; when you read, the OS conveniently 
>remembers when you did. The inconsistency of "writing" to a read-only 
>thing is less important than the inconsistency of not updating the 
>access time when the file is read.
>
>But what if the underlying device is not capable of recording access 
>times, like a CD-ROM? Can you look at the mount options and see that a 
>CDROM is read-only? But then you can't know whether access times will
>be 
>updated unless you use some other method to find out what the
>underlying 
>device is. So that's an abstraction violation. Bother, I don't have a 
>unix box easily to hand where I can check what the mount options on a 
>CDROM look like.
>
>I'm not sure if this is just grousing, or flame bait, or a gotcha that 
>every sysadmin should know because there is no way to anticipate it.
>
>  - Alex
>
>> --Matt
>>
>>
>>
>> On Tue, Dec 3, 2013 at 2:21 PM, Alex Aminoff <alex at basespace.net 
>> <mailto:alex at basespace.net>> wrote:
>>
>>
>>     Hi folks. I encountered something odd.
>>
>>     Suppose you mount a file system read only. You read a file from
>>     it. Does
>>     the access time of that file get updated?
>>
>>     In one place I found documentation saying no. But other places
>seem to
>>     imply that it does.
>>
>>     Does the answer change if it is an NFS mount?
>>
>>     I have deliberately left details of what OS I'm using out,
>because it
>>     seems to me that the answer should be consistent, and if it is
>not, it
>>     should be documented publicly.
>>
>>       - Alex Aminoff
>>         BaseSpace.net, NBER
>>
>>
>>
>>
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>>
>>
>>
>> -- 
>> "Today, vegetables... Tomorrow, the world!"
>>
>>
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