Re: About generic_file_read()

[Fawad Lateef <fawadlateef@xxxxxxxxx>]

On 1/6/06, prasad Musale <prasad.musale@xxxxxxxxx> wrote:
> Hello ,
>  Generic_file_read() reads from cached pages. That means the file pages r
> already in page cache. But if I want to read file from disk, How these pages
> comes in page cache. Ext2 & vfat call this generic_file_read() as their read
> operation. I analyzed the sys_read() code but didn't get how file is read
> from disk. Can anyone tell me about that?

generic_file_read not only reads from the cache but can also do read
from the physical medium (in the case of read-ahead, and cache miss)
and for this it actually calls filp->mappings->a_ops->readpage or
readpages .... which are the function pointers and file systems
assigned it with their functions and normal file-systems like ext2
again from this function calls mpage_readpage function of kernel
(AFAIR) found in mpage.c !

You can see the code of generic_file_read till calling the
a_ops->readpage function  and then consult file-system and the
function called from it like mpage_readpage code.

--
Fawad Lateef

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