On Thu, Oct 11, 2018 at 3:25 PM Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
>
> On Thu, Oct 11, 2018 at 1:24 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> > Implement the FIGETBSZ query with the statfs(2) filesystem
> > interface. Reading inode->i_sb->s_blocksize directly is incorrect
> > on stacked filesystems (i.e. overlayfs).
> >
> > This fixes a Floating point exception in e2fsprogs utility filefrag,
> > which divides the size of the file with the value returned by FIGETBSZ.
> >
> > Fixes: d1d04ef8572b ("ovl: stack file ops")
> > Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> > ---
> >
> > Miklos,
> >
> > Consider this for-rc8?
> > There is another trivial kfree(ERR_PTR()) fix I posted yesterday.
> >
> > xfstests actually has coverage for FIGETBSZ with fiemap-tester
> > program. However, the tests that use fiemap-tester (generic/094
> > generic/225) did not fail on v4.19-rc1, but rather thier runtime
> > dropped from > 10s to 0s, so I'll need to go fix those tests.
> >
> > Thanks,
> > Amir.
> >
> > fs/ioctl.c | 15 ++++++++++++++-
> > 1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/ioctl.c b/fs/ioctl.c
> > index 2005529af560..a0e55a8e94fd 100644
> > --- a/fs/ioctl.c
> > +++ b/fs/ioctl.c
> > @@ -17,6 +17,7 @@
> > #include <linux/buffer_head.h>
> > #include <linux/falloc.h>
> > #include <linux/sched/signal.h>
> > +#include <linux/statfs.h>
> >
> > #include "internal.h"
> >
> > @@ -219,6 +220,18 @@ static int ioctl_fiemap(struct file *filp, unsigned long arg)
> > return error;
> > }
> >
> > +static int ioctl_getbsize(struct file *file, int __user *argp)
> > +{
> > + struct kstatfs buf;
> > + int err;
> > +
> > + err = vfs_statfs(&file->f_path, &buf);
> > + if (err)
> > + return err;
> > +
> > + return put_user(buf.f_bsize, argp);
>
> We must be careful not to change the interface for non-overlayfs while
> trying to fix overlayfs, and I don't see any guarantees, that for
> every other fs f_bsize would be the same as s_blocksize. There are
> other, minor side effects, like possibly blocking and/or generating
> network traffic, unlike the previous version.
>
> But first let's understand what this interface is for. Haven't found
> any other documentation than this:
>
> #define FIGETBSZ _IO(0x00,2) /* get the block size used for bmap */
>
> So it's for the deprecated bmap interface, and we no longer support
> that. Hooray! Then just let's just put some dummy value into
> overlayfs's s_blocksize and s_blocksize_bits (e.g.
> PAGE_SIZE/PAGE_SHIFT) and be done with that.
>
OK. That's fine by me, but notice that filefrag will use the value
it gets from FIGETBSZ even in the FIEMAP implementation,
which is the default implementation.
I think we can set s_blocksize to upper s_blocksize and cover some
common cases. If s_blocksize doesn't match lower s_blocksize we
can warn and set s_blocksize back to 0.
Then, we can return -EINVAL from FIGETBSZ in case s_blocksize
is not set, which is the equivalent of what we do with FIBMAP.
It that too much?
Thanks,
Amir.
