Re: [PATCH 09/29] tools/xenlogd: add 9pfs open request support

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Wed, Nov 1, 2023 at 6:13 AM Juergen Gross <jgross@xxxxxxxx> wrote:
>
> Add the open request of the 9pfs protocol.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  tools/xenlogd/io.c      | 130 ++++++++++++++++++++++++++++++++++++++++
>  tools/xenlogd/xenlogd.h |   4 ++
>  2 files changed, 134 insertions(+)
>
> diff --git a/tools/xenlogd/io.c b/tools/xenlogd/io.c
> index 778e1dc2c9..c2b259f42e 100644
> --- a/tools/xenlogd/io.c
> +++ b/tools/xenlogd/io.c

> @@ -734,6 +745,121 @@ static void p9_walk(device *device, struct p9_header 
> *hdr)
>      free(names);
>  }
>
> +static int open_flags_from_mode(uint8_t mode)
> +{
> +    int flags;
> +
> +    switch ( mode & P9_OMODEMASK )
> +    {
> +    case P9_OREAD:
> +        flags = O_RDONLY;
> +        break;
> +
> +    case P9_OWRITE:
> +        flags = O_WRONLY;
> +        break;
> +
> +    case P9_ORDWR:
> +        flags = O_RDWR;
> +        break;
> +
> +    default:
> +        return -1;
> +    }
> +
> +    if ( mode & P9_OTRUNC )
> +        flags |= O_TRUNC;

"""
In addition, if mode has the OTRUNC (0x10) bit set, the file is to be
truncated, which requires write permission (if the file is
append-only, and permission is granted, the open succeeds but the file
will not be trun- cated);
"""

This relies on libc O_TRUNC handling - I think that is probably better
than something custom so you get the libc semantics.

> +
> +    return flags;
> +}
> +
> +static unsigned int get_iounit(device *device, struct stat *st)
> +{
> +    return (device->max_size - st->st_blksize) & ~(st->st_blksize - 1);
> +}
> +
> +static void p9_open(device *device, struct p9_header *hdr)
> +{
> +    uint32_t fid;
> +    uint8_t mode;
> +    struct p9_fid *fidp;
> +    struct stat st;
> +    struct p9_qid qid;
> +    uint32_t iounit;
> +    int flags;
> +    int ret;
> +
> +    ret = fill_data(device, "Ub", &fid, &mode);
> +    if ( ret != 2 )
> +    {
> +        p9_error(device, hdr->tag, EINVAL);
> +        return;
> +    }
> +    if ( mode & ~(P9_OMODEMASK | P9_OTRUNC | P9_OREMOVE) )
> +    {
> +        p9_error(device, hdr->tag, EINVAL);
> +        return;
> +    }
> +
> +    fidp = find_fid(device, fid);
> +    if ( !fidp )
> +    {
> +        p9_error(device, hdr->tag, ENOENT);

If the host_path points at a populated directory, there is nothing
that populates the fids for pre-existing files and directories?  So
those files cannot be opened?  I guess that's not needed for
Xenstore-stubdom?

Thanks,
Jason