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From:   Chengguang Xu <cgxu519@gmx.com>
To:     gregkh@linuxfoundation.org, dan.carpenter@oracle.com
Cc:     linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
        linux-kernel@vger.kernel.org, Chengguang Xu <cgxu519@gmx.com>
Subject: [PATCH v3 3/4] chardev: code cleanup for __register_chrdev_region()
Date:   Fri,  5 Apr 2019 19:27:10 +0800
Message-Id: <20190405112711.25275-3-cgxu519@gmx.com>
In-Reply-To: <20190405112711.25275-1-cgxu519@gmx.com>
References: <20190405112711.25275-1-cgxu519@gmx.com>
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It's just code cleanup, not functional change.

Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
=2D--
v1->v2:
- Split fix and cleanup patches.
- Remove printing minor range in chrdev_show().

v2->v3:
- Set variable ret to '-EBUSY' before checking minor range overlap.

 fs/char_dev.c | 70 +++++++++++++++++++++------------------------------
 1 file changed, 29 insertions(+), 41 deletions(-)

diff --git a/fs/char_dev.c b/fs/char_dev.c
index 6803e98414f1..47fd0561b03d 100644
=2D-- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -100,10 +100,16 @@ static struct char_device_struct *
 __register_chrdev_region(unsigned int major, unsigned int baseminor,
 			   int minorct, const char *name)
 {
-	struct char_device_struct *cd, **cp;
-	int ret =3D 0;
+	struct char_device_struct *cd, *curr, *prev =3D NULL;
+	int ret;
 	int i;

+	if (major >=3D CHRDEV_MAJOR_MAX) {
+		pr_err("CHRDEV \"%s\" major requested (%u) is greater than the maximum =
(%u)\n",
+		       name, major, CHRDEV_MAJOR_MAX-1);
+		return ERR_PTR(-EINVAL);
+	}
+
 	if (minorct > MINORMASK + 1 - baseminor) {
 		pr_err("CHRDEV \"%s\" minor range requested (%u-%u) is out of range of =
maximum range (%u-%u) for a single major\n",
 			name, baseminor, baseminor + minorct - 1, 0, MINORMASK);
@@ -126,55 +132,37 @@ __register_chrdev_region(unsigned int major, unsigne=
d int baseminor,
 		major =3D ret;
 	}

-	if (major >=3D CHRDEV_MAJOR_MAX) {
-		pr_err("CHRDEV \"%s\" major requested (%u) is greater than the maximum =
(%u)\n",
-		       name, major, CHRDEV_MAJOR_MAX-1);
-		ret =3D -EINVAL;
-		goto out;
-	}
-
-	cd->major =3D major;
-	cd->baseminor =3D baseminor;
-	cd->minorct =3D minorct;
-	strlcpy(cd->name, name, sizeof(cd->name));
-
+	ret =3D -EBUSY;
 	i =3D major_to_index(major);
+	for (curr =3D chrdevs[i]; curr; prev =3D curr, curr =3D curr->next) {
+		if (curr->major < major)
+			continue;

-	for (cp =3D &chrdevs[i]; *cp; cp =3D &(*cp)->next)
-		if ((*cp)->major > major ||
-		    ((*cp)->major =3D=3D major &&
-		     (((*cp)->baseminor >=3D baseminor) ||
-		      ((*cp)->baseminor + (*cp)->minorct > baseminor))))
+		if (curr->major > major)
 			break;

-	/* Check for overlapping minor ranges.  */
-	if (*cp && (*cp)->major =3D=3D major) {
-		int old_min =3D (*cp)->baseminor;
-		int old_max =3D (*cp)->baseminor + (*cp)->minorct - 1;
-		int new_min =3D baseminor;
-		int new_max =3D baseminor + minorct - 1;
+		if (curr->baseminor + curr->minorct <=3D baseminor)
+			continue;

-		/* New driver overlaps from the left.  */
-		if (new_max >=3D old_min && new_max <=3D old_max) {
-			ret =3D -EBUSY;
-			goto out;
-		}
+		if (curr->baseminor >=3D baseminor + minorct)
+			break;

-		/* New driver overlaps from the right.  */
-		if (new_min <=3D old_max && new_min >=3D old_min) {
-			ret =3D -EBUSY;
-			goto out;
-		}
+		goto out;
+	}

-		if (new_min < old_min && new_max > old_max) {
-			ret =3D -EBUSY;
-			goto out;
-		}
+	cd->major =3D major;
+	cd->baseminor =3D baseminor;
+	cd->minorct =3D minorct;
+	strlcpy(cd->name, name, sizeof(cd->name));

+	if (!prev) {
+		cd->next =3D curr;
+		chrdevs[i] =3D cd;
+	} else {
+		cd->next =3D prev->next;
+		prev->next =3D cd;
 	}

-	cd->next =3D *cp;
-	*cp =3D cd;
 	mutex_unlock(&chrdevs_lock);
 	return cd;
 out:
=2D-
2.20.1