This is the mail archive of the
ecos-discuss@sourceware.cygnus.com
mailing list for the eCos project.
RE: I/O driver lookup handler: read/write mode
- To: Masaki Sawanobori <masaki at zentek dot com>
- Subject: RE: [ECOS] I/O driver lookup handler: read/write mode
- From: Gary Thomas <gthomas at cygnus dot co dot uk>
- Date: Tue, 30 Nov 1999 08:47:11 -0700 (MST)
- Cc: ecos-discuss at sourceware dot cygnus dot com
On 30-Nov-99 Masaki Sawanobori wrote:
> Hello,
>
> I am implementing a simple flash memory file system in the framework of eCos
> I/O device driver model and C language libc stdio module so the user can
> access a file using fopen() as follows.
>
> FILE *fp = fopen("/dev/flash0/filename", "r");
> FILE *fp = fopen("/flash0/filename", "w");
>
> The problem is that the second paramter(read/write mode) of fopen() is not
> passed down to a "lookup" device driver handler(via the cyg_io_lookup
> function). The "lookup" handler has no way of returning a correct
> return/error value without knowing whether a file(existing or non-existing)
> is for read or write.
>
I have been thinking along these lines myself. It definitely makes sense
to be able to pass some flags down into 'cyg_io_lookup()', but I'm not sure
I like the idea of strings (mostly because of the overhead). How about
a flag word with bits to indicate the desired state? If you really want/need
to use strings, you could add a layer which handles the translation.
> I would not like to resort to a workaround of adding a read/write mode
> specifier as part of a filename parameter like "/nvram/filename/w" or
> "/nvram/filename/r" or "/nvramR"/filename" or "/nvramW/filename". This
> would be redundant for fopen().
>
This is _not_ the way to go (IMHO).
> Is there any other workaround or a solution for this situation? Am I missing
> something ?
>
Not at this time.
> Here is another wish about I/O device driver handlers. There is no "close"
> handler. I could use a "close" handler since it seems to be a right place
> to free memory allocated in my "lookup" handler.
>
I can also see this having value. I'll look into adding it.
What are you using for your source base? I could see about adding some of
this, but the timing would depend on my/our workload. Perhaps you'd like
to propose some changes and I could review and integrate them? (Not that
I'm trying to get out of work, but that's part of what Open Source is all
about :-)