Re: [PATCH] xfs: allow ro mounts if rtdev or logdev are read-only

[Hans Holmberg <Hans.Holmberg@wdc.com>]

On 28/04/2025 11:52, Carlos Maiolino wrote:
> On Fri, Apr 25, 2025 at 08:52:53AM +0000, Hans Holmberg wrote:
>> Allow read-only mounts on rtdevs and logdevs that are marked as
>> read-only and make sure those mounts can't be remounted read-write.
>>
>> Signed-off-by: Hans Holmberg <hans.holmberg@wdc.com>
>> ---
>>
>> I will post a couple of xfstests to add coverage for these cases.
>>
>>  fs/xfs/xfs_super.c | 24 +++++++++++++++++++++---
>>  1 file changed, 21 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
>> index b2dd0c0bf509..d7ac1654bc80 100644
>> --- a/fs/xfs/xfs_super.c
>> +++ b/fs/xfs/xfs_super.c
>> @@ -380,10 +380,14 @@ xfs_blkdev_get(
>>  	struct file		**bdev_filep)
>>  {
>>  	int			error = 0;
>> +	blk_mode_t		mode;
>>
>> -	*bdev_filep = bdev_file_open_by_path(name,
>> -		BLK_OPEN_READ | BLK_OPEN_WRITE | BLK_OPEN_RESTRICT_WRITES,
>> -		mp->m_super, &fs_holder_ops);
>> +	mode = BLK_OPEN_READ | BLK_OPEN_RESTRICT_WRITES;
> 
> 	Does BLK_OPEN_RESTRICT_WRITES makes sense without BLK_OPEN_WRITE?
> 	Perhaps this should be OR'ed together with OPEN_WRITE below?

BLK_OPEN_RESTRICT_WRITES disallows other writers to mounted devs, and I
presume we want this for read-only mounts as well?

> 
> 
> -Carlos
> 
>> +	if (!xfs_is_readonly(mp))
>> +		mode |= BLK_OPEN_WRITE;
> 
>> +
>> +	*bdev_filep = bdev_file_open_by_path(name, mode,
>> +			mp->m_super, &fs_holder_ops);
>>  	if (IS_ERR(*bdev_filep)) {
>>  		error = PTR_ERR(*bdev_filep);
>>  		*bdev_filep = NULL;
>> @@ -1969,6 +1973,20 @@ xfs_remount_rw(
>>  	struct xfs_sb		*sbp = &mp->m_sb;
>>  	int error;
>>
>> +	if (mp->m_logdev_targp && mp->m_logdev_targp != mp->m_ddev_targp &&
>> +	    bdev_read_only(mp->m_logdev_targp->bt_bdev)) {
>> +		xfs_warn(mp,
>> +			"ro->rw transition prohibited by read-only logdev");
>> +		return -EACCES;
>> +	}
>> +
>> +	if (mp->m_rtdev_targp &&
>> +	    bdev_read_only(mp->m_rtdev_targp->bt_bdev)) {
>> +		xfs_warn(mp,
>> +			"ro->rw transition prohibited by read-only rtdev");
>> +		return -EACCES;
>> +	}
>> +
>>  	if (xfs_has_norecovery(mp)) {
>>  		xfs_warn(mp,
>>  			"ro->rw transition prohibited on norecovery mount");
>> --
>> 2.34.1
>>
>