My personal wishlist

Valery V. Sedletski _valerius at
Mon Apr 1 22:04:37 CEST 2019

On 31.03.2019 23:08, ttcoder at wrote:
> Correction: "Mail" is probably a quite bad example, as it relies 
> heavily on extended attributes. There are probably many candidates all 
> over the difficulty spectrum (from easy to hard) that would make more 
> sense to port. Unless someone came up with a hack to wrap xattr's into 
> something else, ouch.
> Cedric
xattrs? So, Haiku uses Linux terminology? OS/2 calls them "EA's". What 
are extended attributes needed for in Mail
applications? Indexing? Storing keywords? OS/2 mostly uses EA's to store 
object properties for desktop objects, and
also to emulate POSIX file attributes. And also icons, keywords for 
search, tokenized images (i.e., bytecode) for scripts written in REXX 
language etc. In OS/2, EA's are limited in size to at least, 64 KB. With 
JFS, they theoretically could be larger, but for compatibility with 
older HPFS file system, the limit is set to 64 KB. IIRC, in ext2fs, max. 
extended attribute size is only 4 KB, which could be too little for some 
purposes.  In Sculpt, ext2 is used as current file system, so, its 
limits apply. (this is for Linux ext2 driver, not sure about a NetBSD 
driver in rump kernel). On other file sysytems, EA support may be 
missing, but it can be emulated. For example, on FAT, OS/2 uses a file 
called "ea data. sf" in the root directory, which contains EA's of all 
files on the partition in special format. All file metainfo is accessed 
from a directory entry (on FAT), or its inode on most other file 
systems. So, on FAT, a directory entry contains a 16-bit handle to an EA 
stored in "ea data. sf" file. Though, in FAT32 direntry, the two bytes 
used to reference a EA, are reused for high word of first cluster number 
of the file. So, for implementation of EA's in FAT32, two bits of 
another reserved byte of a direntry is reused. (one bit means "this file 
has EA's", another means "the EA's are critical", i.e., they are 
mandatory to be existed when opening the file). So, EA's on FAT32 are 
laying around near the file itself, in the same directory, in a hidden 
file. The disadvantage is that EA files are laying around everywhere, 
like a trash. So, if a file system doesn't support EA's, they can be 
emulated like this.

If I correctly understood, there is no EA/xattr support in Genode VFS, 
so far. But for my project (which is "OS/2 personality" on top of 
Genode), I plan to make a server (like Genode's VFS server) supporting 
OS/2-like IFS (Installable File Systems), like plugins. They, of course, 
support EA's. But then only OS/2 applications will be able to take 
advantage of using EA's. Serving OS/2 file systems to Genode 
applications is planned too. You can go similar way.
> _______________________________________________
> Genode users mailing list
> users at

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the users mailing list