Re: [PATCH v2 04/16] fs: Increase fmode_t size

Jan Kara
2023-12-13T11:20:29Z

On Tue 12-12-23 11:08:32, 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@oracle.com>

Uh, Al has more experience with fmode_t changes so I'd defer final decision
to him but to me this seems dangerous. Firstly, this breaks packing of
struct file on 64-bit architectures and struct file is highly optimized for
cache efficiency (see the comment before the struct definition). Secondly
this will probably generate warnings on 32-bit architectures as there
sizeof(unsigned long) == sizeof(unsigned int) and so your new flags won't
fit anyway?

Honza

> ---
> 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;
>
> #ifdef CONFIG_PHYS_ADDR_T_64BIT
> typedef u64 phys_addr_t;
> --
> 2.35.3
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR