Re: [PATCH v2 1/3] btrfs-progs: Adapt find_mount_root to verify other fields of mntent struct

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2020/11/17 上午1:32, Marcos Paulo de Souza wrote:
> From: Marcos Paulo de Souza <mpdesouza@suse.com>
> 
> Currently find_mount_root searches for all btrfs filesystems
> mounted and comparing <path> with mnt_dir of each mountpoint.
> 
> But there are cases when we need to find the mountpoint for a determined
> subvolid or subvol path, and these informations are present in mnt_opts
> of mntent struct.

Mind to share why we want that?

The main concern here is, I didn't see the point that how the mount
point of a subvolume would affect anything.

Thanks,
Qu

> 
> This patch adds two arguments to find_mount_root (data and flag). The
> data argument hold the information that we want to compare, and the flag
> argument specifies which field of mntent struct that we want to compare.
> Currently there is only one flag, BTRFS_FIND_ROOT_PATH, implementing the
> current behavior. The next patch will add a new flag to expand the functionality.
> 
> Users of find_mount_root were changed, having the data argument the same
> as path, since they are only trying to find the mountpoint based on path alone.
> 
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
> ---
>  cmds/receive.c |  3 ++-
>  cmds/send.c    |  6 ++++--
>  common/utils.c | 15 ++++++++++++---
>  common/utils.h |  8 +++++++-
>  4 files changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/cmds/receive.c b/cmds/receive.c
> index 2aaba3ff..dc64480e 100644
> --- a/cmds/receive.c
> +++ b/cmds/receive.c
> @@ -1079,7 +1079,8 @@ static int do_receive(struct btrfs_receive *rctx, const char *tomnt,
>  	if (realmnt[0]) {
>  		rctx->root_path = realmnt;
>  	} else {
> -		ret = find_mount_root(dest_dir_full_path, &rctx->root_path);
> +		ret = find_mount_root(dest_dir_full_path, dest_dir_full_path,
> +				BTRFS_FIND_ROOT_PATH, &rctx->root_path);
>  		if (ret < 0) {
>  			errno = -ret;
>  			error("failed to determine mount point for %s: %m",
> diff --git a/cmds/send.c b/cmds/send.c
> index b8e3ba12..7757f0da 100644
> --- a/cmds/send.c
> +++ b/cmds/send.c
> @@ -329,7 +329,8 @@ static int init_root_path(struct btrfs_send *sctx, const char *subvol)
>  	if (sctx->root_path)
>  		goto out;
>  
> -	ret = find_mount_root(subvol, &sctx->root_path);
> +	ret = find_mount_root(subvol, subvol, BTRFS_FIND_ROOT_PATH,
> +				&sctx->root_path);
>  	if (ret < 0) {
>  		errno = -ret;
>  		error("failed to determine mount point for %s: %m", subvol);
> @@ -659,7 +660,8 @@ static int cmd_send(const struct cmd_struct *cmd, int argc, char **argv)
>  			goto out;
>  		}
>  
> -		ret = find_mount_root(subvol, &mount_root);
> +		ret = find_mount_root(subvol, subvol, BTRFS_FIND_ROOT_PATH,
> +					&mount_root);
>  		if (ret < 0) {
>  			errno = -ret;
>  			error("find_mount_root failed on %s: %m", subvol);
> diff --git a/common/utils.c b/common/utils.c
> index 1253e87d..1c264455 100644
> --- a/common/utils.c
> +++ b/common/utils.c
> @@ -1248,7 +1248,7 @@ int ask_user(const char *question)
>   * return 1 if a mount point is found but not btrfs
>   * return <0 if something goes wrong
>   */
> -int find_mount_root(const char *path, char **mount_root)
> +int find_mount_root(const char *path, const char *data, u8 flag, char **mount_root)
>  {
>  	FILE *mnttab;
>  	int fd;
> @@ -1258,6 +1258,10 @@ int find_mount_root(const char *path, char **mount_root)
>  	int not_btrfs = 1;
>  	int longest_matchlen = 0;
>  	char *longest_match = NULL;
> +	char *cmp_field = NULL;
> +	bool found;
> +
> +	BUG_ON(flag != BTRFS_FIND_ROOT_PATH);
>  
>  	fd = open(path, O_RDONLY | O_NOATIME);
>  	if (fd < 0)
> @@ -1269,8 +1273,13 @@ int find_mount_root(const char *path, char **mount_root)
>  		return -errno;
>  
>  	while ((ent = getmntent(mnttab))) {
> -		len = strlen(ent->mnt_dir);
> -		if (strncmp(ent->mnt_dir, path, len) == 0) {
> +		cmp_field = ent->mnt_dir;
> +
> +		len = strlen(cmp_field);
> +
> +		found = strncmp(cmp_field, data, len) == 0;
> +
> +		if (found) {
>  			/* match found and use the latest match */
>  			if (longest_matchlen <= len) {
>  				free(longest_match);
> diff --git a/common/utils.h b/common/utils.h
> index 119c3881..449e1d3e 100644
> --- a/common/utils.h
> +++ b/common/utils.h
> @@ -52,6 +52,11 @@
>  #define UNITS_HUMAN			(UNITS_HUMAN_BINARY)
>  #define UNITS_DEFAULT			(UNITS_HUMAN)
>  
> +enum btrfs_find_root_flags {
> +	/* check mnt_dir of mntent */
> +	BTRFS_FIND_ROOT_PATH = 0
> +};
> +
>  void units_set_mode(unsigned *units, unsigned mode);
>  void units_set_base(unsigned *units, unsigned base);
>  
> @@ -93,7 +98,8 @@ int csum_tree_block(struct btrfs_fs_info *root, struct extent_buffer *buf,
>  int ask_user(const char *question);
>  int lookup_path_rootid(int fd, u64 *rootid);
>  int get_btrfs_mount(const char *dev, char *mp, size_t mp_size);
> -int find_mount_root(const char *path, char **mount_root);
> +int find_mount_root(const char *path, const char *data, u8 flag,
> +		char **mount_root);
>  int get_device_info(int fd, u64 devid,
>  		struct btrfs_ioctl_dev_info_args *di_args);
>  int get_df(int fd, struct btrfs_ioctl_space_args **sargs_ret);
> 


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