[ndctl PATCH 02/10] libdaxctl: refactor memblock_is_online() checks

From: Vishal Verma <vishal.l.verma@intel.com>
To: <linux-nvdimm@lists.01.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	Ben Olson <ben.olson@intel.com>,
	Michal Biesek <michal.biesek@intel.com>
Subject: [ndctl PATCH 02/10] libdaxctl: refactor memblock_is_online() checks
Date: Wed,  2 Oct 2019 17:49:17 -0600	[thread overview]
Message-ID: <20191002234925.9190-3-vishal.l.verma@intel.com> (raw)
In-Reply-To: <20191002234925.9190-1-vishal.l.verma@intel.com>

The {online,offline}_one_memblock() helpers both open-coded the check
for whether a block is online. There is already a function to perform
this check - memblock_is_online(). Consolidate the checking using this
helper everywhere it is applicable.

Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 daxctl/lib/libdaxctl.c | 90 +++++++++++++++++-------------------------
 1 file changed, 37 insertions(+), 53 deletions(-)

diff --git a/daxctl/lib/libdaxctl.c b/daxctl/lib/libdaxctl.c
index a828644..6243857 100644
--- a/daxctl/lib/libdaxctl.c
+++ b/daxctl/lib/libdaxctl.c
@@ -1047,12 +1047,11 @@ DAXCTL_EXPORT unsigned long daxctl_memory_get_block_size(struct daxctl_memory *m
 	return mem->block_size;
 }
 
-static int online_one_memblock(struct daxctl_memory *mem, char *memblock)
+static int memblock_is_online(struct daxctl_memory *mem, char *memblock)
 {
 	struct daxctl_dev *dev = daxctl_memory_get_dev(mem);
 	const char *devname = daxctl_dev_get_devname(dev);
 	struct daxctl_ctx *ctx = daxctl_dev_get_ctx(dev);
-	const char *mode = "online_movable";
 	int len = mem->buf_len, rc;
 	char buf[SYSFS_ATTR_SIZE];
 	char *path = mem->mem_buf;
@@ -1073,41 +1072,20 @@ static int online_one_memblock(struct daxctl_memory *mem, char *memblock)
 		return rc;
 	}
 
-	/*
-	 * if already online, possibly due to kernel config or a udev rule,
-	 * there is nothing to do and we can skip over the memblock
-	 */
 	if (strncmp(buf, "online", 6) == 0)
 		return 1;
 
-	rc = sysfs_write_attr_quiet(ctx, path, mode);
-	if (rc) {
-		/*
-		 * While we performed an already-online check above, there
-		 * is still a TOCTOU hole where someone (such as a udev rule)
-		 * may have raced to online the memory. In such a case,
-		 * the sysfs store will fail, however we can check for this
-		 * by simply reading the state again. If it changed to the
-		 * desired state, then we don't have to error out.
-		 */
-		if (sysfs_read_attr(ctx, path, buf) == 0) {
-			if (strncmp(buf, "online", 6) == 0)
-				return 1;
-		}
-		err(ctx, "%s: Failed to online %s: %s\n",
-			devname, path, strerror(-rc));
-	}
-	return rc;
+	/* offline */
+	return 0;
 }
 
-static int offline_one_memblock(struct daxctl_memory *mem, char *memblock)
+static int online_one_memblock(struct daxctl_memory *mem, char *memblock)
 {
 	struct daxctl_dev *dev = daxctl_memory_get_dev(mem);
 	const char *devname = daxctl_dev_get_devname(dev);
 	struct daxctl_ctx *ctx = daxctl_dev_get_ctx(dev);
-	const char *mode = "offline";
+	const char *mode = "online_movable";
 	int len = mem->buf_len, rc;
-	char buf[SYSFS_ATTR_SIZE];
 	char *path = mem->mem_buf;
 	const char *node_path;
 
@@ -1119,37 +1097,39 @@ static int offline_one_memblock(struct daxctl_memory *mem, char *memblock)
 	if (rc < 0)
 		return -ENOMEM;
 
-	rc = sysfs_read_attr(ctx, path, buf);
-	if (rc) {
-		err(ctx, "%s: Failed to read %s: %s\n",
-			devname, path, strerror(-rc));
+	/*
+	 * if already online, possibly due to kernel config or a udev rule,
+	 * there is nothing to do and we can skip over the memblock
+	 */
+	rc = memblock_is_online(mem, memblock);
+	if (rc)
 		return rc;
-	}
-
-	/* if already offline, there is nothing to do */
-	if (strncmp(buf, "offline", 7) == 0)
-		return 1;
 
 	rc = sysfs_write_attr_quiet(ctx, path, mode);
 	if (rc) {
-		/* Close the TOCTOU hole like in online_one_memblock() above */
-		if (sysfs_read_attr(ctx, path, buf) == 0) {
-			if (strncmp(buf, "offline", 7) == 0)
-				return 1;
-		}
-		err(ctx, "%s: Failed to offline %s: %s\n",
+		/*
+		 * While we performed an already-online check above, there
+		 * is still a TOCTOU hole where someone (such as a udev rule)
+		 * may have raced to online the memory. In such a case,
+		 * the sysfs store will fail, however we can check for this
+		 * by simply reading the state again. If it changed to the
+		 * desired state, then we don't have to error out.
+		 */
+		if (memblock_is_online(mem, memblock))
+			return 1;
+		err(ctx, "%s: Failed to online %s: %s\n",
 			devname, path, strerror(-rc));
 	}
 	return rc;
 }
 
-static int memblock_is_online(struct daxctl_memory *mem, char *memblock)
+static int offline_one_memblock(struct daxctl_memory *mem, char *memblock)
 {
 	struct daxctl_dev *dev = daxctl_memory_get_dev(mem);
 	const char *devname = daxctl_dev_get_devname(dev);
 	struct daxctl_ctx *ctx = daxctl_dev_get_ctx(dev);
+	const char *mode = "offline";
 	int len = mem->buf_len, rc;
-	char buf[SYSFS_ATTR_SIZE];
 	char *path = mem->mem_buf;
 	const char *node_path;
 
@@ -1161,18 +1141,22 @@ static int memblock_is_online(struct daxctl_memory *mem, char *memblock)
 	if (rc < 0)
 		return -ENOMEM;
 
-	rc = sysfs_read_attr(ctx, path, buf);
-	if (rc) {
-		err(ctx, "%s: Failed to read %s: %s\n",
-			devname, path, strerror(-rc));
+	/* if already offline, there is nothing to do */
+	rc = memblock_is_online(mem, memblock);
+	if (rc < 0)
 		return rc;
-	}
-
-	if (strncmp(buf, "online", 6) == 0)
+	if (!rc)
 		return 1;
 
-	/* offline */
-	return 0;
+	rc = sysfs_write_attr_quiet(ctx, path, mode);
+	if (rc) {
+		/* Close the TOCTOU hole like in online_one_memblock() above */
+		if (!memblock_is_online(mem, memblock))
+			return 1;
+		err(ctx, "%s: Failed to offline %s: %s\n",
+			devname, path, strerror(-rc));
+	}
+	return rc;
 }
 
 static bool memblock_in_dev(struct daxctl_memory *mem, const char *memblock)
-- 
2.20.1
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