Re: [PATCH 00/68] ide2libata

From: Jeff Garzik
Date: Fri Jan 29 2010 - 16:48:17 EST

On 01/29/2010 11:03 AM, Bartlomiej Zolnierkiewicz wrote:

Here is a patchset (on top of atang-v3.1 tree) applying "out-of-the-box"
thinking to duplicated libata PATA and IDE subsystem host driver sets.
Namely, it modifies IDE API slightly to match libata's one more, adds
a tiny source-code level translation layer (ide2libata.h header file
which consists of only 17 lines of code) and then converts host drivers
to use shared source code for low-level operations (all drivers have
been carefully audited during porting to minimize the probability of
adding regressions accidentally). As an end result it is much easier
to maintain both driver sets (differences between 'new'/'old' drivers
are now apparent and there is no longer a need to manually back-port
many classes of bugfixes) and over 2500 LOC are gone.


I'm fine with applying patches 2-5, but I am definitely interested to hear what others think about this. Clearly, LOC is reduced, but that's not the only factor in code maintenance.

With regards to libata and old-IDE, I have always thought the ideal scenario was to leave old-IDE in bugfix-only mode, with next-to-no API or driver churn besides that which is absolutely required for the fix.

En masse backporting bug fixes is what's known as a one-time cost. Once the majority of libata PATA drivers reach bugfix and feature parity, the need for code sharing is reduced greatly.

The ide2libata proposal creates on-going costs, not just a one-time cost, because the old-IDE drivers will have -increased- potential for problems when a libata PATA driver is modified. Such is the -cost- of heavily intertwined code sharing. A single header change implies that two, not one, drivers might break. That weakens the "leave it alone" stability promise of old-IDE.

Waiting for other comments... this patchset is not an onerous burden to libata, but I think it creates nasty cross-tree issues, potentially perturbing old-IDE.


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