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2024-02-19 890e1df1bec891d9203724541e81f8fbe5183388

 kernel/tools/hv/hv_vss_daemon.c
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..
@@ -1,20 +1,9 @@
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+// SPDX-License-Identifier: GPL-2.0-only
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 /*
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  * An implementation of the host initiated guest snapshot for Hyper-V.
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  *
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- *
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  * Copyright (C) 2013, Microsoft, Inc.
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  * Author : K. Y. Srinivasan <kys@microsoft.com>
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- *
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- * This program is free software; you can redistribute it and/or modify it
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- * under the terms of the GNU General Public License version 2 as published
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- * by the Free Software Foundation.
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- *
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- * This program is distributed in the hope that it will be useful, but
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- * WITHOUT ANY WARRANTY; without even the implied warranty of
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- * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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- * NON INFRINGEMENT.  See the GNU General Public License for more
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- * details.
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- *
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  */
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8
 
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9
 
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@@ -39,6 +28,8 @@
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 #include <stdbool.h>
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 #include <dirent.h>
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+static bool fs_frozen;
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+
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 /* Don't use syslog() in the function since that can cause write to disk */
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 static int vss_do_freeze(char *dir, unsigned int cmd)
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 {
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@@ -53,7 +44,7 @@
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 	 * If a partition is mounted more than once, only the first
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 	 * FREEZE/THAW can succeed and the later ones will get
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 	 * EBUSY/EINVAL respectively: there could be 2 cases:
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-	 * 1) a user may mount the same partition to differnt directories
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+	 * 1) a user may mount the same partition to different directories
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 	 *  by mistake or on purpose;
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 	 * 2) The subvolume of btrfs appears to have the same partition
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 	 * mounted more than once.
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@@ -166,17 +157,26 @@
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 			continue;
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 		}
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 		error |= vss_do_freeze(ent->mnt_dir, cmd);
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-		if (error && operation == VSS_OP_FREEZE)
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-			goto err;
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+		if (operation == VSS_OP_FREEZE) {
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+			if (error)
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+				goto err;
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+			fs_frozen = true;
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+		}
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 	}
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 	endmntent(mounts);
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 	if (root_seen) {
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 		error |= vss_do_freeze("/", cmd);
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-		if (error && operation == VSS_OP_FREEZE)
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-			goto err;
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+		if (operation == VSS_OP_FREEZE) {
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+			if (error)
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+				goto err;
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+			fs_frozen = true;
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+		}
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 	}
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+
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+	if (operation == VSS_OP_THAW && !error)
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+		fs_frozen = false;
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 	goto out;
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 err:
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@@ -186,6 +186,7 @@
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 		endmntent(mounts);
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 	}
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 	vss_operate(VSS_OP_THAW);
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+	fs_frozen = false;
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 	/* Call syslog after we thaw all filesystems */
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 	if (ent)
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 		syslog(LOG_ERR, "FREEZE of %s failed; error:%d %s",
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..
@@ -207,13 +208,13 @@
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 int main(int argc, char *argv[])
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 {
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-	int vss_fd, len;
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+	int vss_fd = -1, len;
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 	int error;
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 	struct pollfd pfd;
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 	int	op;
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 	struct hv_vss_msg vss_msg[1];
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 	int daemonize = 1, long_index = 0, opt;
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-	int in_handshake = 1;
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+	int in_handshake;
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 	__u32 kernel_modver;
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 	static struct option long_options[] = {
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@@ -243,6 +244,18 @@
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 	openlog("Hyper-V VSS", 0, LOG_USER);
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 	syslog(LOG_INFO, "VSS starting; pid is:%d", getpid());
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+reopen_vss_fd:
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+	if (vss_fd != -1)
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+		close(vss_fd);
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+	if (fs_frozen) {
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+		if (vss_operate(VSS_OP_THAW) || fs_frozen) {
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+			syslog(LOG_ERR, "failed to thaw file system: err=%d",
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+			       errno);
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+			exit(EXIT_FAILURE);
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+		}
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+	}
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+
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+	in_handshake = 1;
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 	vss_fd = open("/dev/vmbus/hv_vss", O_RDWR);
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 	if (vss_fd < 0) {
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 		syslog(LOG_ERR, "open /dev/vmbus/hv_vss failed; error: %d %s",
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@@ -295,8 +308,7 @@
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 		if (len != sizeof(struct hv_vss_msg)) {
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 			syslog(LOG_ERR, "read failed; error:%d %s",
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 			       errno, strerror(errno));
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-			close(vss_fd);
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-			return EXIT_FAILURE;
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+			goto reopen_vss_fd;
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 		}
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 		op = vss_msg->vss_hdr.operation;
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@@ -323,14 +335,18 @@
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 		default:
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 			syslog(LOG_ERR, "Illegal op:%d\n", op);
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 		}
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+
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+		/*
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+		 * The write() may return an error due to the faked VSS_OP_THAW
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+		 * message upon hibernation. Ignore the error by resetting the
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+		 * dev file, i.e. closing and re-opening it.
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+		 */
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 		vss_msg->error = error;
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 		len = write(vss_fd, vss_msg, sizeof(struct hv_vss_msg));
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 		if (len != sizeof(struct hv_vss_msg)) {
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 			syslog(LOG_ERR, "write failed; error: %d %s", errno,
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 			       strerror(errno));
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-
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-			if (op == VSS_OP_FREEZE)
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-				vss_operate(VSS_OP_THAW);
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+			goto reopen_vss_fd;
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 		}
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 	}
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