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Re: [PATCH] xfsprogs: skip over "rootfs" entry if mtab links to /proc/mo

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfsprogs: skip over "rootfs" entry if mtab links to /proc/mounts
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Thu, 04 Aug 2011 17:17:40 -0500
Cc: Eric Sandeen <sandeen@xxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <20110803190216.GA31421@xxxxxxxxxxxxx>
References: <4E399677.1010508@xxxxxxxxxx> <20110803190216.GA31421@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:5.0) Gecko/20110624 Thunderbird/5.0
On 8/3/11 2:02 PM, Christoph Hellwig wrote:
> On Wed, Aug 03, 2011 at 01:41:59PM -0500, Eric Sandeen wrote:
>> This is for RH bug 727938, xfs_fsr regression for root file system
>>
>> Fedora has made /etc/mtab a symlink to /proc/mounts, but when
>> we issue "xfs_fsr /" and fsr's getmntany() goes looking for
>> the "/" entry, the first one it finds is
>>
>> rootfs / rootfs rw 0 0
>>
>> it says no way, that's a rootfs filesystem type, not xfs!
>> And it never finds this later:
>>
>> /dev/sda2 / xfs rw,relatime,attr2,noquota 0 0
>>
>> This patch to skip over the rootfs entry seems to fix it.
> 
> I don't like this.  rootfs is the symptom, but the underlying problem
> is that in Linux we're perfectly fine to have multiple filesystems
> mounted on a single mountpoint, and the getmntany can't deal with it.
> 
> I think the right fix is to simply remove the break from the loop,

It's not quite that simple.

when we do

        *mp = *t;
        /* break; */

we are pointing the mp string pointers at the strings in the getmntent entry,
which will keep moving as we iterate.  We'll need a strdup or something
to copy it out on each good find, with appropriate frees etc, I guess.

Is there a better way to do it?  This seems pretty ugly.

        memset(mp, 0, sizeof(struct mntent));
        while ((t = getmntent(fp))) {
                if (mpref->mnt_fsname) {        /* device */
                        if (stat64(t->mnt_fsname, &ms) < 0)
                                continue;
                        if (s->st_rdev != ms.st_rdev)
                                continue;
                }
                if (mpref->mnt_dir) {           /* mount point */
                        if (stat64(t->mnt_dir, &ms) < 0)
                                continue;
                        if (s->st_ino != ms.st_ino || s->st_dev != ms.st_dev)
                                continue;
                }
                /* This one matches */
                found = 1;
                free(mp->mnt_fsname);
                free(mp->mnt_dir);
                free(mp->mnt_type);
                mp->mnt_fsname = strdup(t->mnt_fsname);
                mp->mnt_dir = strdup(t->mnt_dir);
                mp->mnt_type = strdup(t->mnt_type);
        }
        return (found);


(and then free the strings in the caller when we're done ...)

-Eric

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