[maemo-developers] Finding the mmc cards

From: Eero Tamminen eero.tamminen at nokia.com
Date: Wed Aug 29 12:39:37 EEST 2007

Please file a documentation bug into Maemo Bugzilla.  We need this
documented.  Handling of removable medias, especially with file systems
as easily corrupted as FAT, needs special care from applications
(stop using files when pre-unmount message is delivered on them so
that unmounts succeed, do better error handling etc.)

	- Eero

ext maemo-developers-bounces at maemo.org wrote:
> I agree that assuming mmc1 and mmc2 is potentially dangerous. In an answer to my 
> original question on this subject, someone suggested that mmc0 and mmc1 were the 
> correct names, whereas in my Scratchbox environment they are mmc1 and mmc2. 
> Consequently, when I was implementing a scan for memory cards, I opted to look 
> in the /media folder for files whose names begin "mmc", and to assume that any 
> such file I find might be a memory card. This appears to work (in the 
> test/development environment), but personally I hate making those kinds of 
> assumptions. I would far rather have a definitive statement from someone to the 
> effect that "if you do X, this will guarantee to find the memory cards and 
> nothing else". For me, this is particularly important, as my application will be 
> sold commercially and needs to work under all circumstances.
> David Hazel
>   	After our thread some weeks ago regarding reading the serial number from a 
> MMC card, I've since implemented detection of the MMC card's presence by the 
> existence of those same files.  I know my solution works on my device perfectly.
> I figure it's probably a bad decision, because the architecture could change 
> somewhat with the next hardware or software release.
> Can someone tell me, is there an approved / documented way of identifying the 
> location of any MMC cards currently installed?  I've noticed you can't simply 
> look for /media/mmcX because that directory will exist even if there is no card 
> inserted.
> Also, what determines MMC1 vs MMC2 as the card's path for internal/external?  Is 
> it possible these paths would change at some date?  I know some Linux distro's 
> with SATA drives had a problem with the drives changing their /dev/sdX path 
> every reboot.  I know that MY Nokia isn't doing anything similar, but I figure 
> it's possible that my /media/mmc1 might be internal, but for someone else it 
> could be the external slot - or maybe in the next hardware revision or something.
> I did find the alias names located in the /sys/ path that specify "internal" is 
> for one and "external" or removable or something for the other.  Also, are the 
> names and paths the same for the 770's?  Since I have an n800 I don't know.  I'm 
> hesitant to read too much data from /sys/ because it all looks _so_ 
> Maemo-specific I wonder if I will tie my code too closely to one hardware revision.
> Just looking for the most _compatible_ way to identify if/when and where a media 
> card is present.
> And as usual, from Python.
> Thanks,
> Tony

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