On Fri, 5 Oct 2007, Darren J Moffat wrote:
> Alok Aggarwal wrote:
>> On Fri, 5 Oct 2007, Moinak Ghosh wrote:
>>
>>> Alok Aggarwal wrote:
>>>> [...] Examples:
>>>>
>>>> - 1. Compress a file with gzip
>>>> + 1. Compress a file with gzip and add the compressed file as a block
>>>> + device
>>>>
>>>> - # lofiadm -C gzip /export/home/solaris.iso
>>>> + # lofiadm -a -C gzip /export/home/solaris.iso
>>>>
>>>> - 2. Compress a file with gzip and compress it in 64k chunks
>>>> + 2. Compress a file with gzip in 64k chunks and add the compressed
>>>> + file as a block device
>>>>
>>>> # lofiadm -C gzip -s 64k /export/home/solaris.iso
>>>>
>>> Shouldn't this be:
>>>
>>> lofiadm -a -C gzip -s 64k /export/home/solaris.iso
>>> ?
>>
>> It should be, it's a typo.
>
> Now I'm really confused. I thought that the -C was done while there was no
> mapping in place, but -a adds a mapping.
>
>> The original proposal had what you're suggesting, i.e.
>> "compress this file with -C" and "map this compressed file
>> with -a" as a two step process. As part of some offline
>> discussions it was suggested that having these two actions
>> as disjoint steps doesn't buy us anything.
>
> So how long does the compress take ? If it is anything more than a few
> seconds I think it should be a separate step because -a has always been near
> instant.
Yes, it takes a while to compress and depends on the
size of the file being compressed.
>> If a user compresses a file with lofiadm, in all certainity
>> he's bound to map that compressed file as a logical next step
>> so why not just enable him to do that in a single command
>> invocation.
>
> I don't think that follows, in fact given that one of the main motivations
> for this project is building compressed LiveCD images I'd have expected that
> it wouldn't be getting mapped immediately afterwards.
>
> It also incorrectly leads the user into thinking that compression is on the
> fly which it is not.
How does supporting both flavors of the command line
sound? That is -
# lofiadm -C gzip -s 64k /export/home/solaris.iso <-- compress the file
Or, optionally,
# lofiadm -a -C gzip -s 64k /export/home/solaris.iso <-- compress the
file and add it
>> Apropos making compression a separate step so the user doesn't
>> wonder if the command is hung, the lofiadm output will change
>> to printing something like this to stderr (so scripts don't
>> break) -
>
>
>> # lofiadm -a -C gzip -s 64k /export/home/solaris.iso
>> Compressing solaris.iso
>> Mapping solaris.iso
>> /dev/lofi/1
>
> You really shouldn't do that the output of lofiadm -a is intended to be
> scriptable and even says so in the man page:
>
> The ability to specify a device is pro-
> vided for use in scripts that wish to
> re-establish a particular set of asso-
> ciations.
Will the scripts still break if the new messages "Compressing
file" and "Mapping file" are sent to *stderr* though?
"/dev/lofi/1" still goes to stdout so there should be no
difference from the scripts' perspective.
> The other problem with -C being part of the mapping is it is now different
> from the -U option to uncompress since you wouldn't do lofiadm -d -U
Supporting both forms of the command line should take care
of this.
Alok
