Re: [Minios-devel] [UNIKRAFT PATCH v2 4/5] lib/vfscore: do not advance position for stdio

[Florian Schmidt <Florian.Schmidt@xxxxxxxxx>]

Hi Yuri,

On 6/3/19 11:04 AM, Yuri Volchkov wrote:
> With the proper handling of uio for stdio files, vfs also advances the
> position in the struct file. Which does not make any sense for console
> (and some other classes of devices).
>
> This patch adds another flags variable inside struct
> vfscore_file. Using f_flags would add more mess in the code, because
> most of the flags are defined in fcntl.h, which is external from
> vfscore header.
>
> Signed-off-by: Yuri Volchkov <yuri.volchkov@xxxxxxxxx>
> ---
>   lib/vfscore/fops.c                 | 3 ++-
>   lib/vfscore/include/vfscore/file.h | 3 +++
>   lib/vfscore/stdio.c                | 1 +
>   3 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/lib/vfscore/fops.c b/lib/vfscore/fops.c
> index 79114e21..ad78d3b1 100644
> --- a/lib/vfscore/fops.c
> +++ b/lib/vfscore/fops.c
> @@ -107,7 +107,8 @@ int vfs_write(struct vfscore_file *fp, struct uio *uio, int 
> flags)
>         error = VOP_WRITE(vp, uio, ioflags);
>         if (!error) {
>                 count = bytes - uio->uio_resid;
> -               if ((flags & FOF_OFFSET) == 0)
> +               if (!(flags & FOF_OFFSET) &&
> +                   !(fp->f_vfs_flags & UK_VFSCORE_NOPOS))
>                         fp->f_offset += count;
>         }
>   
> diff --git a/lib/vfscore/include/vfscore/file.h b/lib/vfscore/include/vfscore/file.h
> index 2c0252e2..be1c7772 100644
> --- a/lib/vfscore/include/vfscore/file.h
> +++ b/lib/vfscore/include/vfscore/file.h
> @@ -46,12 +46,15 @@ extern "C" {
>   
>   struct vfscore_file;
>   
> +#define UK_VFSCORE_NOPOS ((int) (1 << 0))
> +
I was scratching my head here wondering what a NOP-OS is, until I 
realized (and it took me way longer that it should have!) that it's 
about NO-POS(isition information). Maybe explain that really quickly in 
the code for other people who are as slow as me. ;-)
As a side note: the lwip<->vfscore then should probably also set this on 
lwip sockets? Since they are also not seekable and don't have a "file 
position"?
>   struct vfscore_file {
>         int fd;
>         int             f_flags;        /* open flags */
>         int             f_count;        /* reference count */
>         off_t           f_offset;       /* current position in file */
>         void            *f_data;        /* file descriptor specific data */
> +       int             f_vfs_flags;    /* internal implementation flags */
>         struct dentry   *f_dentry;
>   };
>   
> diff --git a/lib/vfscore/stdio.c b/lib/vfscore/stdio.c
> index 8e3ccbdb..40288bb3 100644
> --- a/lib/vfscore/stdio.c
> +++ b/lib/vfscore/stdio.c
> @@ -144,6 +144,7 @@ static struct vfscore_file  stdio_file = {
>         .fd = 1,
>         .f_flags = UK_FWRITE | UK_FREAD,
>         .f_dentry = &stdio_dentry,
> +       .f_vfs_flags = UK_VFSCORE_NOPOS,
>         /* reference count is 2 because close(0) is a valid
>          * operation. However it is not properly handled in the
>          * current implementation. */
--
Dr. Florian Schmidt
フローリアン・シュミット
Research Scientist,
Systems and Machine Learning Group
NEC Laboratories Europe
Kurfürsten-Anlage 36, D-69115 Heidelberg
Tel.     +49 (0)6221 4342-265
Fax:     +49 (0)6221 4342-155
e-mail:  florian.schmidt@xxxxxxxxx
============================================================
Registered at Amtsgericht Mannheim, Germany, HRB728558

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