Re: [PATCH] GFS2: minor readability improvement in gfs2_mount()

Steven Whitehouse
2013-06-10T11:07:21Z

Hi,

On Fri, 2013-06-07 at 10:49 +0400, Alexey Khoroshilov wrote:
> Hi Steve,
>
> On 06/06/2013 01:24 PM, Steven Whitehouse wrote:
> > Hi,
> >
> > On Thu, 2013-06-06 at 01:29 +0400, Alexey Khoroshilov wrote:
> >> The patch makes usage pattern of IS_ERR-PTR_ERR more typical.
> >>
> >> Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
> >> ---
> >> fs/gfs2/ops_fstype.c | 5 +++--
> >> 1 file changed, 3 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
> >> index 0262c19..0d30e8e 100644
> >> --- a/fs/gfs2/ops_fstype.c
> >> +++ b/fs/gfs2/ops_fstype.c
> >> @@ -1313,9 +1313,10 @@ static struct dentry *gfs2_mount(struct file_system_type *fs_type, int flags,
> >> }
> >> s = sget(fs_type, test_gfs2_super, set_gfs2_super, flags, bdev);
> >> mutex_unlock(&bdev->bd_fsfreeze_mutex);
> >> - error = PTR_ERR(s);
> >> - if (IS_ERR(s))
> >> + if (IS_ERR(s)) {
> >> + error = PTR_ERR(s);
> >> goto error_bdev;
> >> + }
> > I'm not sure what you are getting at here. Why add a jump into the fast
> > path?
> My experiments with gcc 4.7.3 on x86-64 do not show any difference in
> code generated with patch and without it.
> 227a: e8 00 00 00 00 callq 227f <gfs2_mount+0xb1>
> 227b: R_X86_64_PC32 sget-0x4
> 227f: 4c 89 f7 mov %r14,%rdi
> 2282: 49 89 c4 mov %rax,%r12
> 2285: e8 00 00 00 00 callq 228a <gfs2_mount+0xbc>
> 2286: R_X86_64_PC32 mutex_unlock-0x4
> 228a: 49 81 fc 00 f0 ff ff cmp $0xfffffffffffff000,%r12
> 2291: 0f 87 2a 01 00 00 ja 23c1 <gfs2_mount+0x1f3>
> 2297: 49 83 7c 24 60 00 cmpq $0x0,0x60(%r12)
> 229d: 74 0b je 22aa <gfs2_mount+0xdc>
> 229f: 44 89 ee mov %r13d,%esi
> 22a2: 48 89 df mov %rbx,%rdi
> 22a5: e8 00 00 00 00 callq 22aa <gfs2_mount+0xdc>
> 22a6: R_X86_64_PC32 blkdev_put-0x4
>
> It looks like 'error = PTR_ERR(s);' assignment is just ignored because s and error share the same register %r12.
>
> So the only point of the patch is to improve readability.
>
Hmm, ok. I'm still not convinced that it does really improve readability
in this case I'm afraid, so I'm not going to apply this one,

Steve.

> --
> Best regards,
> Alexey