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SubjectRe: [PATCH 09/11] sysfs: Push file_update_time() into bin_page_mkwrite()
Jan Kara <jack@suse.cz> writes:

> On Thu 16-02-12 13:04:44, Alex Elder wrote:
>> On Thu, 2012-02-16 at 14:46 +0100, Jan Kara wrote:
>> > CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> > Signed-off-by: Jan Kara <jack@suse.cz>
>> > ---
>> > fs/sysfs/bin.c | 2 ++
>> > 1 files changed, 2 insertions(+), 0 deletions(-)
>> >
>> > diff --git a/fs/sysfs/bin.c b/fs/sysfs/bin.c
>> > index a475983..6ceb16f 100644
>> > --- a/fs/sysfs/bin.c
>> > +++ b/fs/sysfs/bin.c
>> > @@ -225,6 +225,8 @@ static int bin_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
>> > if (!sysfs_get_active(attr_sd))
>> > return VM_FAULT_SIGBUS;
>> >
>> > + file_update_time(file);
>> > +
>> > ret = 0;
>> > if (bb->vm_ops->page_mkwrite)
>> > ret = bb->vm_ops->page_mkwrite(vma, vmf);
>>
>> If the filesystem's page_mkwrite() function is responsible
>> for updating the time, can't the call to file_update_time()
>> here be conditional?
>>
>> I.e:
>> ret = 0;
>> if (bb->vm_ops->page_mkwrite)
>> ret = bb->vm_ops->page_mkwrite(vma, vmf);
>> else
>> file_update_time(file);
> Hmm, I didn't look previously where do we get bb->vm_ops. It seems they
> are inherited from vma->vm_ops so what you suggest should be safe without
> any further changes. So I can do that if someone who understands the sysfs
> code likes it more.

I do. Essentially sysfs is being a stackable filesystem here, because
sysfs needs the ability to remove a file mapping.

In practice we could probably get away without a single
file_update_time(file) here because there are mmio mappings. Normally
for pci resources, but we might as well use good form since we can.

Eric


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