[lxc-devel] [lxc/master] rootfs pinning: On NFS, make file hidden but don't delete it

[gjaekel on Github]

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From 63fc76c3e0d90bc6a3d9ea82a91b3fbc8a3552ef Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Guido=20J=C3=A4kel?= <g.jaekel at dnb.de>
Date: Fri, 6 Apr 2018 09:35:21 +0200
Subject: [PATCH] rootfs pinning: On NFS, make file hidden but don't delete it

On NFS, avoid random names of the root pin file due to "NFS silly renaming" but use a fixed hidden name instead.
---
 src/lxc/conf.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/lxc/conf.c b/src/lxc/conf.c
index 745584308..6e0b06a00 100644
--- a/src/lxc/conf.c
+++ b/src/lxc/conf.c
@@ -539,10 +539,11 @@ int run_script(const char *name, const char *section, const char *script, ...)
 }
 
 /* pin_rootfs
- * if rootfs is a directory, then open ${rootfs}/lxc.hold for writing for
+ * if rootfs is a directory, then open ${rootfs}/.lxc-keep for writing for
  * the duration of the container run, to prevent the container from marking
  * the underlying fs readonly on shutdown. unlink the file immediately so
- * no name pollution is happens
+ * no name pollution is happens.
+ * don't unlink on NFS to avoid random named stale handles.
  * return -1 on error.
  * return -2 if nothing needed to be pinned.
  * return an open fd (>=0) if we pinned it.
@@ -552,6 +553,7 @@ int pin_rootfs(const char *rootfs)
 	int fd, ret;
 	char absrootfs[MAXPATHLEN], absrootfspin[MAXPATHLEN];
 	struct stat s;
+	struct statfs sfs;
 
 	if (rootfs == NULL || strlen(rootfs) == 0)
 		return -2;
@@ -570,7 +572,7 @@ int pin_rootfs(const char *rootfs)
 	if (!S_ISDIR(s.st_mode))
 		return -2;
 
-	ret = snprintf(absrootfspin, MAXPATHLEN, "%s/lxc.hold", absrootfs);
+	ret = snprintf(absrootfspin, MAXPATHLEN, "%s/.lxc-keep", absrootfs);
 	if (ret >= MAXPATHLEN)
 		return -1;
 
@@ -578,6 +580,15 @@ int pin_rootfs(const char *rootfs)
 	if (fd < 0)
 		return fd;
 
+	if (fstatfs (fd, &sfs)) {
+		return -1;
+	}
+
+	if (sfs.f_type == NFS_SUPER_MAGIC) {
+		DEBUG("rootfs on NFS, not unlinking pin file \"%s\".", absrootfspin);
+		return fd;
+	}
+
 	(void)unlink(absrootfspin);
 
 	return fd;