Re: buffer head and buffer pages

[Ravi Krishnamurthy <kravi26@yahoo.com>]

--- "Raghu R. Arur" <rra2002@aria.ncl.cs.columbia.edu>
wrote:
>   Hi,
> 
>   Please help me to understand this better. each buffer
> has a buffer
> head. the b_page of buffer_head points to the page that
> contains the
> mapped data. Will both these pages ( the page that holds
> the buffer_head
> structure and buffer page that contains the actual data)
> mapped to the
> process OR only the page with the buffer_head is mapped
> to the process ?

 The buffer head is never mapped into user address space.
It is a kernel data structure and doesn't have to be
accessed from userspace.
 The buffer itself holds data from a file. If the file
is mmap'ed (or is executable code), then the page is
mapped into user space. If the file is accessed using
read/write, then it isn't.

Hope this helps,
Ravi.

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