Andrew Lunn wrote:
On Sat, Nov 15, 2008 at 04:56:56PM +0100, Rutger Hofman wrote:
Good afternoon list,
I am making good progress with YAFFS on top of the eCos NAND Flash
library; I can mkdir/rmdir, opendir/readdir, rename, open/creat/unlink,
read/write files, and walk the directory tree on my NAND flash chip.
Now, one thing I am unhappy about is file/directory permissions. YAFFS
has permissions (user/group/other a la POSIX), but eCos has no chmod()
call. In old exchanges on this list I saw this crop up on FAT, but FAT's
attributes are different from (POSIX) file permissions. Some guru back
then advised an implementation of chmod() that calls cyg_fs_setinfo()
with a FS_INFO_CHMOD tag. But this route was not taken: I see no chmod()
anywhere.
Would it be a good idea that I add chmod() to file.cxx/fileio.h that
does take the above route, and implement it by having it call
cyg_fs_setinfo() with a tag FS_INFO_CHMOD? My guess is that this
shouldn't break the other filesystems, they would return an error code
on an unknown tag FS_INFO_CHMOD.
The problem with permissions is that they require a concept of a user
identity. eCos does not have this. There is no uid to know if the user
owns the file. There is no group of users to know if the group
permissions are valid. So how do you decide which of the ugo bits to
look at?
Without a concept of ugo, how is YAFFS even using the ugo permission?
I feel that in eCos chmod() is pointless...
Yes, certainly it's correct that ugo does not make very much sense in eCos.
But:
- my aim is that YAFFS filesystems can also be approached from u-boot,
uCLinux, Linux, ..., even if they are created by eCos; Linux and friends
do support ugo;
- even if there is no ugo, a permissions notion might make sense. So, if
the mask is 000 there is no permission at all. 777 would allow everything;
- eCos has open()/creat() with permissions. It has stat() with
permissions. It has access() with permissions. Ruling out chmod()
because permissions don't make sense for chmod() seems not completely
consistent;
- of course I can make an fs-private flag FS_YAFFS_INFO_CHMOD and call
cyg_fs_setinfo() from the application. I do not feel attracted to that
in comparison with having chmod(), because it makes the fs type manifest
to the application.
Rutger
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