On Wednesday, February 21, 2018 6:31:55 AM IST Eric Biggers wrote:
> Hi Chandan,
>
> On Mon, Feb 12, 2018 at 03:13:41PM +0530, Chandan Rajendra wrote:
> > With block size < page size, ext4_block_write_begin() can have up to two
> > blocks to decrypt. Hence this commit invokes fscrypt_decrypt_block() for
> > each of those blocks.
> >
> > Signed-off-by: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx>
> > ---
> > fs/ext4/inode.c | 33 +++++++++++++++++++++++----------
> > 1 file changed, 23 insertions(+), 10 deletions(-)
> >
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 69a4fd6..180dd2d 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -1158,12 +1158,13 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
> > unsigned to = from + len;
> > struct inode *inode = page->mapping->host;
> > unsigned block_start, block_end;
> > - sector_t block;
> > + sector_t block, page_blk_nr;
> > int err = 0;
> > unsigned blocksize = inode->i_sb->s_blocksize;
> > unsigned bbits;
> > struct buffer_head *bh, *head, *wait[2], **wait_bh = wait;
> > bool decrypt = false;
> > + int i;
> >
> > BUG_ON(!PageLocked(page));
> > BUG_ON(from > PAGE_SIZE);
> > @@ -1224,18 +1225,30 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
> > /*
> > * If we issued read requests, let them complete.
> > */
> > - while (wait_bh > wait) {
> > - wait_on_buffer(*--wait_bh);
> > - if (!buffer_uptodate(*wait_bh))
> > + for (i = 0; &wait[i] < wait_bh; i++) {
> > + wait_on_buffer(wait[i]);
> > + if (!buffer_uptodate(wait[i]))
> > err = -EIO;
> > }
>
> [...]
>
> > + for (i = 0; &wait[i] < wait_bh; i++) {
> > + int err2;
> > +
> > + --wait_bh;
> > + block = page_blk_nr + (bh_offset(wait[i]) >> bbits);
> > + err2 = fscrypt_decrypt_block(page->mapping->host, page,
> > + wait[i]->b_size,
> > + bh_offset(wait[i]),
> > + block);
> > + if (err2) {
> > + clear_buffer_uptodate(wait[i]);
> > + err = err2;
> > + }
> > + }
>
> These are very confusing ways to iterate through an array, especially the second
> loop which is actually going in reverse order (why?). Why not just use a
> variable like 'nr_wait' for the number of valid buffer_head's like I had
> suggested? Then you can just do 'for (i = 0; i < nr_wait; i++)'.
>
Sorry, the "--wait_bh;" part was a remanent from the "RFC PATCH V1". Without
that statement, we loop in increasing order of elements in wait[] array. I
will use the 'nr_wait' counter approach and post the next version of the
patchset. I misunderstood your advice to mean that the code should use
similar looping order in both loops.
--
chandan
