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Subject: Re: [PATCH] [nfs-utils] fix method to check if mounted already
To:     "Jianhong.Yin" <yin-jianhong@163.com>
Cc:     linux-nfs@vger.kernel.org
References: <20181025041518.24465-1-yin-jianhong@163.com>
From:   Steve Dickson <SteveD@RedHat.com>
Message-ID: <81f5caf3-c802-4563-7924-53259e875369@RedHat.com>
Date:   Thu, 25 Oct 2018 11:38:16 -0400
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Hello,

On 10/25/18 12:15 AM, Jianhong.Yin wrote:
> reproducer:
> '''
> mkdir /expdir /mnt/nfsmp /mnt/tmpfs
> echo "/expdir *(rw,no_root_squash)" >/etc/exports
> service nfs restart
> mount -t tmpfs tmpfs /mnt/tmpfs
> mount -osharecache localhost:/expdir /mnt/nfsmp #success
> mount -osharecache localhost:/expdir /mnt/nfsmp #mounted already, return 0(pass)
> mount -osharecache localhost:/expdir /mnt/tmpfs #success
> mount -osharecache localhost:/expdir /mnt/tmpfs #mounted already, return 0(pass)
> umount /mnt/nfsmp
> umount /mnt/tmpfs
> 
> mount -ocontext=system_u:object_r:xferlog_t:s0,sharecache localhost:/expdir /mnt/nfsmp
> mount -ocontext=system_u:object_r:user_home_dir_t:s0,sharecache localhost:/expdir /mnt/tmpfs
> [[ $? = 0 ]] && echo "***test fail: hasn't mounted, should return fail ***"
> '''
> 
> Signed-off-by: Jianhong Yin <yin-jianhong@163.com>
> ---
>  support/include/misc.h    |  1 +
>  support/misc/mountpoint.c | 26 +++++++++++++++++++++++++-
>  utils/mount/stropts.c     |  4 +---
>  3 files changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/support/include/misc.h b/support/include/misc.h
> index 06e2a0c..6a146e4 100644
> --- a/support/include/misc.h
> +++ b/support/include/misc.h
> @@ -19,6 +19,7 @@ char *generic_make_pathname(const char *, const char *);
>  _Bool generic_setup_basedir(const char *, const char *, char *, const size_t);
>  
>  extern int is_mountpoint(char *path);
> +extern int is_mounted_already(const char *fsname, const char *dir);
>  
>  /* size of the file pointer buffers for rpc procfs files */
>  #define RPC_CHAN_BUF_SIZE 32768
> diff --git a/support/misc/mountpoint.c b/support/misc/mountpoint.c
> index 9f9ce44..e21d529 100644
> --- a/support/misc/mountpoint.c
> +++ b/support/misc/mountpoint.c
> @@ -4,8 +4,10 @@
>   */
>  
>  #include <string.h>
> -#include "xcommon.h"
>  #include <sys/stat.h>
> +#include <stdio.h>
> +#include <mntent.h>
> +#include "xcommon.h"
>  #include "misc.h"
>  
>  int
> @@ -38,3 +40,25 @@ is_mountpoint(char *path)
>  	free(dotdot);
>  	return rv;
>  }
> +
> +int
> +is_mounted_already(const char *fsname, const char *dir)
> +{
> +	struct mntent *ent;
> +	FILE *fp;
> +	int ret = 0;
> +
> +	fp = setmntent("/proc/mounts", "r");
> +	if (fp == NULL) {
> +		perror("[unlikely] setmntent(3) fail");
> +		exit(1);
> +	}
> +	while (NULL != (ent = getmntent(fp))) {
> +		if (!strcmp(ent->mnt_fsname, fsname) && !strcmp(ent->mnt_dir, dir)) {
> +			ret = 1;
> +			break;
> +		}
> +	}
> +	endmntent(fp);
> +	return ret;
> +}
This does not scale on a large machines, especially when all that
is needed is two stat()s... one on the directory and one on the 
parent directory.

> diff --git a/utils/mount/stropts.c b/utils/mount/stropts.c
> index eed0356..0ee13bc 100644
> --- a/utils/mount/stropts.c
> +++ b/utils/mount/stropts.c
> @@ -1079,9 +1079,7 @@ static int nfsmount_fg(struct nfsmount_info *mi)
>  		if (nfs_try_mount(mi))
>  			return EX_SUCCESS;
>  
> -#pragma GCC diagnostic ignored "-Wdiscarded-qualifiers"
> -		if (errno == EBUSY && is_mountpoint(mi->node))
> -#pragma GCC diagnostic warning "-Wdiscarded-qualifiers"
> +		if (errno == EBUSY && is_mounted_already(mi->spec, mi->node))
>  			/*
>  			 * EBUSY can happen when mounting a filesystem that
>  			 * is already mounted or when the context= are
> 
This has been fixed with commit 2e5533976c76c1

steved.