linux-kernel - Re: [PATCH v2 04/16] fs: Increase fmode

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Date:   Wed, 13 Dec 2023 13:15:39 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     Christian Brauner <brauner@...nel.org>
Cc:     axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
        viro@...iv.linux.org.uk, dchinner@...hat.com, jack@...e.cz,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-scsi@...r.kernel.org, ming.lei@...hat.com,
        jaswin@...ux.ibm.com, bvanassche@....org
Subject: Re: [PATCH v2 04/16] fs: Increase fmode_t size

On 13/12/2023 13:02, Christian Brauner wrote:
> On Tue, Dec 12, 2023 at 11:08:32AM +0000, John Garry wrote:
>> Currently all bits are being used in fmode_t.
>>
>> To allow for further expansion, increase from unsigned int to unsigned
>> long.
>>
>> Since the dma-buf driver prints the file->f_mode member, change the print
>> as necessary to deal with the larger size.
>>
>> Signed-off-by: John Garry <john.g.garry@...cle.com>
>> ---
>>   drivers/dma-buf/dma-buf.c | 2 +-
>>   include/linux/types.h     | 2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
>> index 21916bba77d5..a5227ae3d637 100644
>> --- a/drivers/dma-buf/dma-buf.c
>> +++ b/drivers/dma-buf/dma-buf.c
>> @@ -1628,7 +1628,7 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
>>   
>>   
>>   		spin_lock(&buf_obj->name_lock);
>> -		seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\t%08lu\t%s\n",
>> +		seq_printf(s, "%08zu\t%08x\t%08lx\t%08ld\t%s\t%08lu\t%s\n",
>>   				buf_obj->size,
>>   				buf_obj->file->f_flags, buf_obj->file->f_mode,
>>   				file_count(buf_obj->file),
>> diff --git a/include/linux/types.h b/include/linux/types.h
>> index 253168bb3fe1..49c754fde1d6 100644
>> --- a/include/linux/types.h
>> +++ b/include/linux/types.h
>> @@ -153,7 +153,7 @@ typedef u32 dma_addr_t;
>>   
>>   typedef unsigned int __bitwise gfp_t;
>>   typedef unsigned int __bitwise slab_flags_t;
>> -typedef unsigned int __bitwise fmode_t;
>> +typedef unsigned long __bitwise fmode_t;
> 
> As Jan said, that's likely a bad idea. There's a bunch of places that
> assume fmode_t is 32bit. So not really a change we want to make if we
> can avoid it.

ok, understood.

Some strictly unnecessary bits in f_mode could be recycled (if there 
were any), but this issue will prob come up again.

Could it be considered to add an extended fmode_t member in struct file?

Thanks,
John