Re: Flash erase groups and filesystems

[Pierre Ossman <drzeus-list@drzeus.cx>]

Jörn Engel wrote:

>Question came up before, albeit with a different phrasing.  One
>possible approach to benefit from this ability would be to create a
>"forget" operation.  When a filesystem already knows that some data is
>unneeded (after a truncate or erase operation), it will ask the device
>to forget previously occupied blocks.
>
>The device then has the _option_ of handling the forget operation.
>Further reads on these blocks may return random data.
>
>And since noone stepped up to implement this yet, you can still get
>all the fame and glory yourself! ;)
>  
>

I'm not sure we're talking about the same thing. I'm not suggesting new
features in the VFS layer. I want to know if something breaks if I
implement this erase feature in the MMC layer. In essence the file
system has marked the sectors as "forget" by issuing a write to them.
The question is if it is assumed that they are unchanged if the write
fails half-way through.

I'd have to say that this is a dangerous assumption to make already
today since some systems might not be able to tell where it fails if a
large chunk of data is given to it, perhaps because of a deep pipeline
before it actually reaches the physical storage.

Rgds
Pierre