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SubjectRe: [PATCH] mm: do_generic_file_read() never gets a NULL 'filp' argument
Hi Andrew,

> > > > The 'filp' argument to do_generic_file_read() is never NULL.
> > >
> > > How did you verify this?
> > >
> > > NFS used to like passing NULL file*'s into VFS functions. I don't
> > > recall whether it affected do_generic_file_read().
> >
> > The only thing nfsd passed a NULL file pointer in is ->fsync on
> > directories.
>
> NFS, not NFSD. It was page_cache_read(), iirc.

Is it important?
Cristoph wrote following decision reason at last mail.
I believe he was right.

> If anyone did pass a NULL file pointer into
> do_generic_file_read it would oops in it's very first line of code.


IOW, do_generic_file_read() has following calling hieralcy.

generic_file_aio_read()
+- do_generic_file_read()

and fs/nfs/file.c has

const struct file_operations nfs_file_operations = {
.llseek = nfs_file_llseek,
.read = do_sync_read,
.write = do_sync_write,
.aio_read = nfs_file_read,
.aio_write = nfs_file_write,

So, nfs doesn't use generic_file_aio_read.
it directly indicate nfs doesn't use do_generic_file_read().

in the other hand, page_cache_read() has following calling hieralcy.

filemap_fault()
+- page_cache_read()
+- a_ops->readpage()

So, page_cache_read is mmap() related helper function and
do_generic_file_read is read() related helper function.
they are independent IMHO.




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