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.
Thanks,
Miklos
