linux-kernel - Re: [PATCH -next] binder: simplify the return expression of binder

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Message-ID: <20200921080830.vrki7dcm64l46ppb@wittgenstein>
Date:   Mon, 21 Sep 2020 10:08:30 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Liu Shixin <liushixin2@...wei.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <christian@...uner.io>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] binder: simplify the return expression of
 binder_mmap

On Mon, Sep 21, 2020 at 04:24:23PM +0800, Liu Shixin wrote:
> Simplify the return expression.
> 
> Signed-off-by: Liu Shixin <liushixin2@...wei.com>
> ---

Why not is all I can really say. :) But if this is about simplifying you
could get rid of the "ret" and "failure string" variables, and the goto
in that function completely by doing sm like this (__completely
untested__):

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index f936530a19b0..26f4dc81b008 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -5182,9 +5182,7 @@ static const struct vm_operations_struct binder_vm_ops = {

 static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
 {
-       int ret;
        struct binder_proc *proc = filp->private_data;
-       const char *failure_string;

        if (proc->tsk != current->group_leader)
                return -EINVAL;
@@ -5196,9 +5194,9 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
                     (unsigned long)pgprot_val(vma->vm_page_prot));

        if (vma->vm_flags & FORBIDDEN_MMAP_FLAGS) {
-               ret = -EPERM;
-               failure_string = "bad vm_flags";
-               goto err_bad_arg;
+               pr_err("%s: %d %lx-%lx %s failed %d\n", __func__,
+                               proc->pid, vma->vm_start, vma->vm_end, "bad vm_flags", -EPERM);
+               return -EPERM;
        }
        vma->vm_flags |= VM_DONTCOPY | VM_MIXEDMAP;
        vma->vm_flags &= ~VM_MAYWRITE;
@@ -5206,15 +5204,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
        vma->vm_ops = &binder_vm_ops;
        vma->vm_private_data = proc;

-       ret = binder_alloc_mmap_handler(&proc->alloc, vma);
-       if (ret)
-               return ret;
-       return 0;
-
-err_bad_arg:
-       pr_err("%s: %d %lx-%lx %s failed %d\n", __func__,
-              proc->pid, vma->vm_start, vma->vm_end, failure_string, ret);
-       return ret;
+       return binder_alloc_mmap_handler(&proc->alloc, vma);
 }

Christian