[Cluster-devel] [PATCH 1/3] libgfs2: Add lgfs2_open_mnt* functions

[Steven Whitehouse]

Hi,

That looks much better I than what we had before I think. Thanks for
sorting that out,

Steve.

On Sat, 2013-11-16 at 20:11 +0000, Andrew Price wrote:
> 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.
> 
> Signed-off-by: Andrew Price <anprice at redhat.com>
> ---
>  gfs2/libgfs2/libgfs2.h |  4 +++
>  gfs2/libgfs2/misc.c    | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 98 insertions(+)
> 
> 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;