btrfs: allow mounting btrfs subvolumes with different ro/rw options
Given the following /etc/fstab entries: /dev/sda3 /mnt/foo btrfs subvol=foo,ro 0 0 /dev/sda3 /mnt/bar btrfs subvol=bar,rw 0 0 you can't issue: $ mount /mnt/foo $ mount /mnt/bar You would have to do: $ mount /mnt/foo $ mount -o remount,rw /mnt/foo $ mount --bind -o remount,ro /mnt/foo $ mount /mnt/bar or $ mount /mnt/bar $ mount --rw /mnt/foo $ mount --bind -o remount,ro /mnt/foo With this patch you can do $ mount /mnt/foo $ mount /mnt/bar $ cat /proc/self/mountinfo 49 33 0:41 /foo /mnt/foo ro,relatime shared:36 - btrfs /dev/sda3 rw,ssd,space_cache 87 33 0:41 /bar /mnt/bar rw,relatime shared:74 - btrfs /dev/sda3 rw,ssd,space_cache Signed-off-by: Chris Mason <clm@fb.com>
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@ -66,6 +66,8 @@
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static const struct super_operations btrfs_super_ops;
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static struct file_system_type btrfs_fs_type;
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static int btrfs_remount(struct super_block *sb, int *flags, char *data);
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static const char *btrfs_decode_error(int errno)
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{
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char *errstr = "unknown";
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@ -1185,6 +1187,26 @@ static struct dentry *mount_subvol(const char *subvol_name, int flags,
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mnt = vfs_kern_mount(&btrfs_fs_type, flags, device_name,
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newargs);
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kfree(newargs);
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if (PTR_RET(mnt) == -EBUSY) {
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if (flags & MS_RDONLY) {
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mnt = vfs_kern_mount(&btrfs_fs_type, flags & ~MS_RDONLY, device_name,
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newargs);
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} else {
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int r;
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mnt = vfs_kern_mount(&btrfs_fs_type, flags | MS_RDONLY, device_name,
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newargs);
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if (IS_ERR(mnt))
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return ERR_CAST(mnt);
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r = btrfs_remount(mnt->mnt_sb, &flags, NULL);
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if (r < 0) {
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/* FIXME: release vfsmount mnt ??*/
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return ERR_PTR(r);
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}
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}
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}
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if (IS_ERR(mnt))
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return ERR_CAST(mnt);
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