commit 3c8db52fe77267109a6f01c178370747a23e64fd

Author: Andrew Price <anprice@redhat.com>

Date:   Sat Nov 16 02:10:52 2013 -0600

    libgfs2: Add lgfs2_open_mnt* functions

    lgfs2_open_mnt is a replacement for is_pathname_mounted which tries to reduce

    races by opening paths speculatively and passing back the open fds once they're

    known to be correct. lgfs2_open_mnt_{dev,dir} build on this to provide a

    convenient way to open just the device or mount directory relating to a path

    which could be either.

    Resolves: bz#991204

    Signed-off-by: Andrew Price <anprice@redhat.com>

diff --git a/gfs2/libgfs2/libgfs2.h b/gfs2/libgfs2/libgfs2.h

index f864a08..3e5d09c 100644

--- a/gfs2/libgfs2/libgfs2.h

+++ b/gfs2/libgfs2/libgfs2.h

@@ -12,6 +12,7 @@

 #include <linux/limits.h>

 #include <endian.h>

 #include <byteswap.h>

+#include <mntent.h>

 #include <linux/gfs2_ondisk.h>

 #include "osi_list.h"

@@ -715,6 +716,9 @@ extern int compute_heightsize(struct gfs2_sbd *sdp, uint64_t *heightsize,

 		uint32_t *maxheight, uint32_t bsize1, int diptrs, int inptrs);

 extern int compute_constants(struct gfs2_sbd *sdp);

 extern int is_pathname_mounted(char *path_name, char *device_name, int *ro_mount);

+extern int lgfs2_open_mnt(const char *path, int dirflags, int *dirfd, int devflags, int *devfd, struct mntent **mnt);

+extern int lgfs2_open_mnt_dev(const char *path, int flags, struct mntent **mnt);

+extern int lgfs2_open_mnt_dir(const char *path, int flags, struct mntent **mnt);

 extern int find_gfs2_meta(struct gfs2_sbd *sdp);

 extern int dir_exists(const char *dir);

 extern int mount_gfs2_meta(struct gfs2_sbd *sdp);

diff --git a/gfs2/libgfs2/misc.c b/gfs2/libgfs2/misc.c

index 7f500e6..195b983 100644

--- a/gfs2/libgfs2/misc.c

+++ b/gfs2/libgfs2/misc.c

@@ -163,6 +163,100 @@ int is_pathname_mounted(char *path_name, char *device_name, int *ro_mount)

 	return 1; /* mounted */

 }

+/* Returns 0 if fd1 and fd2 refer to the same device/file, 1 otherwise, or -1 on error */

+static int fdcmp(int fd1, int fd2)

+{

+	struct stat st1, st2;

+	if ((fstat(fd1, &st1) != 0) || (fstat(fd2, &st2) != 0))

+		return -1;

+	if (S_ISBLK(st1.st_mode) && S_ISBLK(st2.st_mode)) {

+		if (st1.st_rdev == st2.st_rdev) {

+			return 0;

+		}

+	} else if ((st1.st_dev == st2.st_dev) && (st1.st_ino == st2.st_ino)) {

+			return 0;

+	}

+	return 1;

+}

+

+int lgfs2_open_mnt(const char *path, int dirflags, int *dirfd, int devflags, int *devfd, struct mntent **mnt)

+{

+	FILE *fp = setmntent("/proc/mounts", "r");

+	if (fp == NULL) {

+		perror("open: /proc/mounts");

+		return 1;

+	}

+	/* Assume path is mount point until we know better. */

+	*dirfd = open(path, dirflags);

+	if (*dirfd < 0)

+		return 1;

+

+	while ((*mnt = getmntent(fp)) != NULL) {

+		int fd;

+		if (strcmp((*mnt)->mnt_type, "gfs2") != 0)

+			continue;

+		*devfd = open((*mnt)->mnt_fsname, devflags);

+		/* Defer checking *devfd until later: whether it's ok to ignore

+		 * the error depends on whether we find the mount point. */

+

+		if (strcmp(path, (*mnt)->mnt_dir) == 0)

+			break;

+		if (strcmp(path, (*mnt)->mnt_fsname) == 0 || fdcmp(*dirfd, *devfd) == 0) {

+			/* We have a match but our above assumption was

+			   incorrect and *dirfd is actually the device. */

+			close(*dirfd);

+			*dirfd = open((*mnt)->mnt_dir, dirflags);

+			break;

+		}

+

+		fd = open((*mnt)->mnt_dir, dirflags);

+		if (fd >= 0) {

+			int diff = fdcmp(*dirfd, fd);

+			close(fd);

+			if (diff == 0)

+				break;

+		}

+		if (*devfd >= 0)

+			close(*devfd);

+	}

+	endmntent(fp);

+	if (*mnt == NULL) {

+		close(*dirfd);

+		return 0; /* Success. Answer is no. Both fds closed. */

+	}

+	if (*dirfd < 0) {

+		close(*devfd);

+		return 1;

+	}

+	if (*devfd < 0) {

+		close(*dirfd);

+		return 1;

+	}

+	return 0; /* Success. Answer is yes. Both fds open. */

+}

+

+int lgfs2_open_mnt_dev(const char *path, int flags, struct mntent **mnt)

+{

+	int dirfd = -1;

+	int devfd = -1;

+	if (lgfs2_open_mnt(path, O_RDONLY, &dirfd, flags, &devfd, mnt) != 0)

+		return -1;

+	if (*mnt != NULL)

+		close(dirfd);

+	return devfd;

+}

+

+int lgfs2_open_mnt_dir(const char *path, int flags, struct mntent **mnt)

+{

+	int dirfd = -1;

+	int devfd = -1;

+	if (lgfs2_open_mnt(path, flags, &dirfd, O_RDONLY, &devfd, mnt) != 0)

+		return -1;

+	if (*mnt != NULL)

+		close(devfd);

+	return dirfd;

+}

+

 static int lock_for_admin(struct gfs2_sbd *sdp)

 {

 	int error;