Basic CVS from Emacs

I've been a long time user of Emacs both on UNIX/Linux and on Windows, and I'm reasonably proficient now I suppose - I have a small set of keyboard short cuts that I use regularly for things like switching between buffers and doing query-replace operations - but I'm aware that I've only scratched the surface of what the program is capable of (after all, I still think it's "just" an editor).

So my most recent discovery is probably not news to a lot of people, but I still think it's pretty neat: specifically, the ability to access CVS version control operations on a file directly from within Emacs using its standard version control interface, vc.el.

A quick summary of the basics: to load vc.el and activate the functions, first do Ctrl-x Ctrl-q, then:

• Use the sequence Ctrl-x v = to see differences between the current buffer and the last CVS version (i.e. cvs diff), and
  
• Use the sequence Ctrl-x v v to commit your changes - this opens a new buffer to write the commit message, and when you're done use Ctrl-c Ctrl-c to finish the commit.

Other operations are available but I think these are the ones that will be most useful to me, as it means I won't need to leave the editor in order to commit changes from the command line. (Also with this method I don't need to "revert" the buffer after CVS has updated any keywords in the file, which I always have to do when using editor-plus-command-line.)

So far I've been using this with GNU Emacs 22.2.1 and CVS 1.12.3 on Ubuntu Linux. I'm guessing that Emacs works out that the file is under version control by detecting the CVS subdirectory, and that the same (or similar) key sequences might also work for SVN - but I have no idea yet if this will work on Windows using Xemacs and TortoiseCVS (I will report back once I've had a chance to investigate further).

Stormy weather? Cloud Computing caveats

The concept of "cloud computing" suddenly seems to be going mainstream - as well as receiving several emails advertising Sitepoint's latest book "Host Your Website in the Cloud" (about how to use Amazon's cloud computing platform AWS), I've seen a whole bunch of articles and events about various aspects of the Cloud - not all of them uncritical (for example Dai Davis' BCS talk I previously reported).

Today I came across another article, "Cloud Computing caveats" by James Hayes (on the IET website) which draws attention to some of the issues that businesses should perhaps be considering before rushing to use cloud-based services. Ignoring the first cavaet ("Is it new?"), which really just gives a brief history of how today's cloud evolved from what went before (summary: internet connections have only recently achieved the capacity and resilience required to make them possible), the remaining concerns are much the same as those expressed in Dai's talk:

1. Data ownership: once you put your data into the cloud, you've given up a degree of control. Do you understand the implications, and are they acceptable both legally and operationally?
   
2. Service level agreements: if the service becomes unavailable for some reason, what reassurances do you have from your cloud provider about how long it will take to put it right? What would the impact of downtime be on your business?
   
3. Risk appraisal: cloud services might have a low up-front cost that is particularly attractive to smaller enterprises, but have they properly assessed the risks (and potential costs - not just financial) if the service encounters problems?
   
4. "Cloud governance": in the traditional model of enterprise software procurement, a company's IT department could exercise a high degree of control over what software was used there. The ease of access to cloud computing services offering equivalent functionality threatens to bypass these controls (including assessments of longer term costs and risks).
   

The software geek inside me finds the technical aspects of cloud computing technology absolutely fascinating (which is why I want to get the Sitepoint book, even though I don't really need it), and as a consumer I'm using all kinds of cloud-based services. But my internal project manager recognises that it's also vital important to understand any wider implications of a particular technology used in a specific context - best summed up by a quote from one of the people interviewed in James's article: "None of the risks associated with Cloud are 'showstoppers' for all enterprises and for all specific use cases within any single enterprise ... but they will be for some."

Simple distributed version control using Dropbox

Over the last 2 years I've been developing a few personal software projects, and while I'd happily been using CVS for version control on one machine (a laptop running Windows XP), there were two significant friction points: 1) how to transfer code to my other machines (I'm running two other separate operating systems - Ubuntu Linux and Windows XP - on a single dual-booting desktop PC), and then merge any changes or fixes back again, and 2) how to ensure that the CVS repositories were being regularly and reliably backed up.

One of the issues with the first problem is that while it's irritating and error-prone to work around (and has a deterrent effect on performing cross-system testing), it doesn't cause enough real pain to force you to properly deal with it. The second problem is that hardy perennial, that making back ups never really feels that urgent (until immediately after your hard drive fails).

So I had been limping along for a while until a few months ago when I read an article called "Easy Version Control" by Ryan Taylor (havocinspired.co.uk) in August's .net magazine. Ryan's article covers a lot of other things, but for me the key suggestion is to use the free Dropbox file synchronisation service (which also provides you with up to 2GB of online storage) to back up and share the version control repositories.

The actual set up process is simple:

1. Install the Dropbox client on the first machine,
2. Put your repositories inside the special Dropbox directory/folder that is created when the client is installed,
3. Install Dropbox clients on each of the other machines where you want to access the repositories.

The Dropbox clients do the rest: they automatically synchronise the Dropbox directories/folders - including the repositories - across all machines. You can then check out working copies of your code and commit changes back to the repository on any machine, which will be automatically reflected on all the others. Additionally, a synchronised copy of the repository is also held on the Dropbox servers (thus taking care of the back up issue).

In Ryan's article he works with SVN rather than CVS but this doesn't appear to be a problem - neither does sharing repositories between Linux and Windows (where I'm using TortoiseCVS ). (He also suggests that several people could work with the same repository at once by enabling sharing in Dropbox for the appropriate directories/folders.) So all in all this seems like an ideal solution for simple distributed version control for personal projects like mine.

Social and Legal Aspects of Cloud Computing

Last week I attended one of the public talks organised by the Manchester branch of the BCS, by Dai Davis of Brooke North LLP, entitled "Social and Legal Aspects of Cloud Computing".

Dai's definition of "cloud computing" was quite broad - essentially it's the delivery of a service over the internet, where encompassing "software as a service" through to "storage as a service" and "platform as a service". You could think of it as "renting" hardware, software and/or data storage. The most obvious example is web mail - the service provider typically gives you access to an email client and also handles storage and retrieval of your email.

A key characteristic of cloud computing is that the hardware and data storage could be physically located anywhere in the world, and as an end user you have no idea where they are - you're leaving the service provider to deal with the technical details - and for this reason, cloud computing services have undeniable attractions at the point of entry: they usually have low start-up costs for the end user, both financially and in terms of ease-of-use.

However Dai suggested that there are other factors to consider before opting to use these services, and central to this is control of data - your data. As already noted, once you've entered your data into the system you have no idea where is in the world. Do you know who else might have access to it? If you try to delete it, how do you know if it's really gone? And what if you want to get your data out again - can you get it in the format you need? The first three of these are potential issues under the EU Data Protection legislation, which forbids export of personal data outside the EU, only allows it to be held for as long as is necessary to process it, and stipulates that you must take appropriate measures to ensure its security.

Unfortunately you are unlikely to have any legally-binding guarantees from the service provider as regards any of these - you're asked to take it on trust that the service provider won't abuse their position of trust. Dai pointed to last year's incident when Amazon unilaterally removed copies of "1984" from customers' Kindles as an indication of what could happen, but there are other issues with people losing control of their data - posting to Facebook being one example (another interesting aside was Dai's observation that although it is possible to delete your Facebook account, it's very difficult to erase all trace of yourself from it).

Ultimately the choice about using cloud computing-based services is then a risk-reward analysis, and the problem is really that although the benefits are usually obvious, the risks only become evident further down the line. It's possible that we're yet to realise the full implications of these things. I don't think that Dai is saying that we shouldn't use these services, only that we should go in with our eyes open. Overall, a fascinating and slightly worrying overview of the issues.

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This is my blog dedicated specifically to my interests in software development. It's a bit of an experiment and I'm not sure how I'll get on with it, however if you're reading this then welcome!