On Thu, May 26, 2022 at 10:43:51PM -0700, Christoph Hellwig wrote:
> > static ssize_t jfs_quota_read(struct super_block *sb, int type, char *data,
> > + size_t len, loff_t pos)
> > {
> > struct inode *inode = sb_dqopt(sb)->files[type];
> > + struct address_space *mapping = inode->i_mapping;
> > size_t toread;
> > + pgoff_t index;
> > loff_t i_size = i_size_read(inode);
> >
> > + if (pos > i_size)
> > return 0;
> > + if (pos + len > i_size)
> > + len = i_size - pos;
> > toread = len;
> > + index = pos / PAGE_SIZE;
> > +
> > while (toread > 0) {
> > + struct folio *folio = read_mapping_folio(mapping, index, NULL);
> > + size_t tocopy = PAGE_SIZE - offset_in_page(pos);
> > + void *src;
> > +
> > + if (IS_ERR(folio))
> > + return PTR_ERR(folio);
> > +
> > + src = kmap_local_folio(folio, offset_in_folio(folio, pos));
> > + memcpy(data, src, tocopy);
> > + kunmap_local(src);
>
> It would be great to have a memcpy_from_folio like the existing
> memcpy_from_page for this.
Yes, I agree. It could copy more than a single page like
zero_user_segments() does.
> > + folio_put(folio);
> >
> > toread -= tocopy;
> > data += tocopy;
> > + pos += tocopy;
> > + index++;
> > }
> > return len;
>
> And this whole helper is generic now. It might be worth to move it
> into fs/quota/dquot.c as generic_quota_read.
I was thinking it was filemap_read_kernel(inode, pos, dst, len)
but perhaps both of these things ...
