Re: [RFC] ioctl vs xattr for the filesystem specific attributes

[Rob North]

OGAWA Hirofumi wrote:
> Hi,
>
> Bastien Roucaries <roucariesbastien@xxxxxxxx> writes:
>
>
> > This patch implement an "extended attributes" (XATTR) hook in aim to read or
> > modify specific  fatfs flags' like ARCHIVE or SYSTEM.
> >
> > I believe it's a good idea  because :
> > 	- PAX ( GNU replacement of tar) save and restore XATTRs, so you can make more
> > exact save of FATfs without use of specific programs.
> > 	- It's an elegant means to avoid use of mattrib.
> > 	- Samba can use this .
> > but CONS :
> > 	- use 2 Kb of kernel memory.
>
>
> Bastien Roucaries <roucariesbastien@xxxxxxxx> writes:
>
>
> > Indeed some flags are shared by many namespace for instance immutable is 
> > shared by xfs,ext2/3,jfs and by the fat ( with a special mount option). 
> > Compress also is a very common flag
> > This flags are in the "common" sub-namespace.
> >
> > But some are fs specifics for instance notail attr of reiserfs,shortname of 
> > fat.They are in the the "spec"sub-namespace
>
>
> I received the above email.
>
> This read/modify the file attributes of filesystem specific via xattr
> interface (in this case, ARCHIVE, SYSTEM, HIDDEN flags of fatfs).
>
> Yes, also we can provide it via ioctl like ext2/ext3 does now.
>
> But if those flags provides by xattr interfaces and via one namespace
> prefix, I guess the app can save/restore easy without dependency of
> one fs.
>
> Which interface would we use for attributes of filesystem specific?
> Also if we use xattr, what namepace prefix should be used?
>
> Any idea?
>
> Thanks.


I like the ideas that the patch seems to propose.
Infact I'd like to see the use of xattr used for non-standard attributes
applied to all fs.
Specifically, I want to backup all partitions, and attribs from one OS:
Linux. I do not want to loose fat attributes during backup.
This would also be useful for the Wine developers.


If you haven't got a response to your questions, maybe make your own 
decisions and submit a patch anyway.


One question:
How does the patch deal with the fact that only some named xattrs are
permitted?

I see 2 options:
1. all files/dirs in fat mount posess fat-specific xattrs. These xattrs 
are initialised at file/dir create. No further attribs can be added, 
none can be deleted. the fat attribute's Boolean value is defined by 
extended attribute's value.
2. all fat-specific attribs are optional, absence/presence defines
boolean value. All operations are permitted, but can only add the
fat-specific attributes.

I prefer option 1, as it makes clear what attributes are available.


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