read actor

read actor

[fcorneli]

Hi,

When one uses do_generic_file_read to (in-kernel) read a file from the 
page cache one has to give a read_actor as parameter. Suppose different 
do_generic_file_read instances occur simultaneously, then how can a 
shared file_read_actor differentiate between the different 
do_generic_file_read instances that made a call to it?
Shouldn't read_descriptor_t contain something like
	void *this_data;
to make this possible?

I also very much could use a this_data field so my read_actor can put the 
data into a structure pointed to by this_data.
If something for this already is present somewhere... please point me to 
that place in the code tree.

Please CC me; I'm not on the list.


Frank.

Re: read actor

[Christoph Hellwig]

On Thu, Apr 03, 2003 at 04:14:05PM +0200, fcorneli@elis.ugent.be wrote:
> Hi,
> 
> When one uses do_generic_file_read to (in-kernel) read a file from the 
> page cache one has to give a read_actor as parameter. Suppose different 
> do_generic_file_read instances occur simultaneously, then how can a 
> shared file_read_actor differentiate between the different 
> do_generic_file_read instances that made a call to it?
> Shouldn't read_descriptor_t contain something like
> 	void *this_data;
> to make this possible?

do_generic_file_read is not an interface you are supposed to use, and any use
of it will lead to subtile races with filesystems that use the pagecache
but not plain generic_file_read.  See the ->sendfile operation in 2.5
for a proper fix.