lkml.org 
[lkml]   [2002]   [Feb]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: O_DIRECT fails in some kernel and FS
Chris Mason wrote:

>
>On Saturday, February 02, 2002 08:54:38 PM +0100 Andrea Arcangeli <andrea@suse.de> wrote:
>
>>>Chris and I had initially decided to unpack the tails on file open
>>>if O_DIRECT is used, but it seems cleaner to add a
>>>reiserfs_get_block_direct_io, and have it return -EINVAL if a read
>>>went to a tail. writes that happen to a tail will trigger tail
>>>conversion.
>>>
>>This is a safe approch (no risk of corruption etc..). However to provide
>>the same semantics of the other filesystems it would be even better if
>>we could unpack the tail within reiserfs_get_block_direct_io rather than
>>returning -EINVAL, but ok, most apps should work fine anyways (and as
>>worse people can workaround the magic by remounting reiserfs with notail
>>before writing the data that will need to be handled later via
>>O_DIRECT).
>>
>
>In the normal case, O_DIRECT can't be done on a file with a tail.
>
>The way I read generic_file_direct_IO, O_DIRECT is only done in
>units that start block aligned, and continue for a block aligned
>length. So, this can never include a packed file tail.
>
>We should only need to worry if i_size on the file is wrong, and allows a
>read/write to a block aligned chunk on a file with a tail, which should
>only be legal in the expanding truncate case from older kernels. The
>-EINVAL return should only happen in this (very unlikely) case.
>
>-chris
>
Can't you fall back to buffered I/O for the tail? OK it complicates the
code, probably a lot, but it keeps things sane from the user's point of
view.

Steve



-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:23    [W:0.071 / U:0.324 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site