linux-kernel - [PATCH 1/5] Tools: hv: vss: Skip freezing filesystems backed by loop

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Date:   Sun,  6 Aug 2017 13:12:52 -0700
From:   kys@...hange.microsoft.com
To:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
        vkuznets@...hat.com, jasowang@...hat.com,
        leann.ogasawara@...onical.com, marcelo.cerri@...onical.com,
        sthemmin@...rosoft.com
Cc:     Alex Ng <alexng@...sages.microsoft.com>,
        Vyronas Tsingaras <vyronas@...ingaras.me>,
        "K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 1/5] Tools: hv: vss: Skip freezing filesystems backed by loop

From: Alex Ng <alexng@...sages.microsoft.com>

Since a loop device is backed by a file, a backup will already result in
its parent filesystem being frozen. It's sufficient to just freeze the
parent filesystem, so we can skip the loop device.

This avoids a situation where a loop device and its parent filesystem are
both frozen and then thawed out of order. For example, if the loop device
is enumerated first, we would thaw it while its parent filesystem is still
frozen. The thaw operation fails and the loop device remains frozen.

Signed-off-by: Alex Ng <alexng@...sages.microsoft.com>
Signed-off-by: Vyronas Tsingaras <vyronas@...ingaras.me>
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
---
 tools/hv/hv_vss_daemon.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/tools/hv/hv_vss_daemon.c b/tools/hv/hv_vss_daemon.c
index 7ba5419..b2b4ebf 100644
--- a/tools/hv/hv_vss_daemon.c
+++ b/tools/hv/hv_vss_daemon.c
@@ -21,6 +21,7 @@
 #include <sys/types.h>
 #include <sys/poll.h>
 #include <sys/ioctl.h>
+#include <sys/stat.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <mntent.h>
@@ -30,6 +31,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <linux/fs.h>
+#include <linux/major.h>
 #include <linux/hyperv.h>
 #include <syslog.h>
 #include <getopt.h>
@@ -70,6 +72,7 @@ static int vss_operate(int operation)
 	char match[] = "/dev/";
 	FILE *mounts;
 	struct mntent *ent;
+	struct stat sb;
 	char errdir[1024] = {0};
 	unsigned int cmd;
 	int error = 0, root_seen = 0, save_errno = 0;
@@ -92,6 +95,10 @@ static int vss_operate(int operation)
 	while ((ent = getmntent(mounts))) {
 		if (strncmp(ent->mnt_fsname, match, strlen(match)))
 			continue;
+		if (stat(ent->mnt_fsname, &sb) == -1)
+			continue;
+		if (S_ISBLK(sb.st_mode) && major(sb.st_rdev) == LOOP_MAJOR)
+			continue;
 		if (hasmntopt(ent, MNTOPT_RO) != NULL)
 			continue;
 		if (strcmp(ent->mnt_type, "vfat") == 0)
-- 
1.7.1