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.
> 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.
> 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.
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
--
Darren J Moffat
