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authorGeorge Melikov <mail@gmelikov.ru>2017-01-26 23:28:29 +0300
committerBrian Behlendorf <behlendorf1@llnl.gov>2017-01-26 12:28:29 -0800
commit774ee3c7cec223521f41a4c533f2561da43ee425 (patch)
treed31d6f7ec373f0cf705c530c117164891c5976aa /lib/libzfs/libzfs_mount.c
parentf925de3a20e97d3b9ee854c8435c6f3d8d17e02c (diff)
OpenZFS 7336 - vfork and O_CLOEXEC causes zfs_mount EBUSY
Porting notes: - statvfs64 is replaced by statfs64. - ZFS_SUPER_MAGIC definition moved in include/sys/fs/zfs.h to share it between user and kernel space. Authored by: Prakash Surya <prakash.surya@delphix.com> Reviewed by: Matt Ahrens <mahrens@delphix.com> Reviewed by: Paul Dagnelie <pcd@delphix.com> Reviewed by: Robert Mustacchi <rm@joyent.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Ported-by: George Melikov <mail@gmelikov.ru> OpenZFS-issue: https://www.illumos.org/issues/7336 OpenZFS-commit: https://github.com/openzfs/openzfs/commit/dd862f6d Closes #5651
Diffstat (limited to 'lib/libzfs/libzfs_mount.c')
-rw-r--r--lib/libzfs/libzfs_mount.c68
1 files changed, 62 insertions, 6 deletions
diff --git a/lib/libzfs/libzfs_mount.c b/lib/libzfs/libzfs_mount.c
index 5fc96f1ab..312724d4d 100644
--- a/lib/libzfs/libzfs_mount.c
+++ b/lib/libzfs/libzfs_mount.c
@@ -75,6 +75,7 @@
#include <sys/mntent.h>
#include <sys/mount.h>
#include <sys/stat.h>
+#include <sys/vfs.h>
#include <libzfs.h>
@@ -170,13 +171,32 @@ is_shared(libzfs_handle_t *hdl, const char *mountpoint, zfs_share_proto_t proto)
return (SHARED_NOT_SHARED);
}
-/*
- * Returns true if the specified directory is empty. If we can't open the
- * directory at all, return true so that the mount can fail with a more
- * informative error message.
- */
static boolean_t
-dir_is_empty(const char *dirname)
+dir_is_empty_stat(const char *dirname)
+{
+ struct stat st;
+
+ /*
+ * We only want to return false if the given path is a non empty
+ * directory, all other errors are handled elsewhere.
+ */
+ if (stat(dirname, &st) < 0 || !S_ISDIR(st.st_mode)) {
+ return (B_TRUE);
+ }
+
+ /*
+ * An empty directory will still have two entries in it, one
+ * entry for each of "." and "..".
+ */
+ if (st.st_size > 2) {
+ return (B_FALSE);
+ }
+
+ return (B_TRUE);
+}
+
+static boolean_t
+dir_is_empty_readdir(const char *dirname)
{
DIR *dirp;
struct dirent64 *dp;
@@ -206,6 +226,42 @@ dir_is_empty(const char *dirname)
}
/*
+ * Returns true if the specified directory is empty. If we can't open the
+ * directory at all, return true so that the mount can fail with a more
+ * informative error message.
+ */
+static boolean_t
+dir_is_empty(const char *dirname)
+{
+ struct statfs64 st;
+
+ /*
+ * If the statvfs call fails or the filesystem is not a ZFS
+ * filesystem, fall back to the slow path which uses readdir.
+ */
+ if ((statfs64(dirname, &st) != 0) ||
+ (st.f_type != ZFS_SUPER_MAGIC)) {
+ return (dir_is_empty_readdir(dirname));
+ }
+
+ /*
+ * At this point, we know the provided path is on a ZFS
+ * filesystem, so we can use stat instead of readdir to
+ * determine if the directory is empty or not. We try to avoid
+ * using readdir because that requires opening "dirname"; this
+ * open file descriptor can potentially end up in a child
+ * process if there's a concurrent fork, thus preventing the
+ * zfs_mount() from otherwise succeeding (the open file
+ * descriptor inherited by the child process will cause the
+ * parent's mount to fail with EBUSY). The performance
+ * implications of replacing the open, read, and close with a
+ * single stat is nice; but is not the main motivation for the
+ * added complexity.
+ */
+ return (dir_is_empty_stat(dirname));
+}
+
+/*
* Checks to see if the mount is active. If the filesystem is mounted, we fill
* in 'where' with the current mountpoint, and return 1. Otherwise, we return
* 0.