Re: [PATCH 08/16] hw/9pfs: Handle current directory offset for Windows

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Monday, October 24, 2022 6:57:51 AM CET Bin Meng wrote:
> From: Guohuai Shi <guohuai.shi@windriver.com>
> 
> On Windows 'struct dirent' does not have current directory offset.
> We have to save current directory offset and update offset when
> reading directory.
> 
> Signed-off-by: Guohuai Shi <guohuai.shi@windriver.com>
> Signed-off-by: Bin Meng <bin.meng@windriver.com>
> ---
> 
>  hw/9pfs/9p.c    | 16 ++++++++++++++++
>  hw/9pfs/codir.c | 15 +++++++++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index aebadeaa03..6c4af86240 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -2319,7 +2319,15 @@ static int coroutine_fn v9fs_do_readdir_with_stat(V9fsPDU *pdu,
>          count += len;
>          v9fs_stat_free(&v9stat);
>          v9fs_path_free(&path);
> +#ifndef CONFIG_WIN32
>          saved_dir_pos = qemu_dirent_off(dent);
> +#else
> +        /*
> +         * Get offset by calling telldir() manually,
> +         * as Windows does not have dent->d_off.
> +         */
> +        saved_dir_pos = v9fs_co_telldir(pdu, fidp);
> +#endif
>      }

That's not the way to go. We already had the same discussion with the macOS
patches and why we introduced qemu_dirent_off() for exactly that purpose:

v9fs_co_telldir() would dispatch the coroutine from QEMU main thread to
background worker thread and vice versa. So you would get side effects by
doing this.

Please implement this adequately in qemu_dirent_off() instead of touching the
controller portion here.

>  
>      v9fs_readdir_unlock(&fidp->fs.dir);
> @@ -2520,7 +2528,15 @@ static int coroutine_fn v9fs_do_readdir(V9fsPDU *pdu, V9fsFidState *fidp,
>              qid.version = 0;
>          }
>  
> +#ifndef CONFIG_WIN32
>          off = qemu_dirent_off(dent);
> +#else
> +        /*
> +         * Get offset by calling telldir() manually,
> +         * as Windows does not have dent->d_off.
> +         */
> +        off = v9fs_co_telldir(pdu, fidp);
> +#endif
>          v9fs_string_init(&name);
>          v9fs_string_sprintf(&name, "%s", dent->d_name);
>  
> diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c
> index 93ba44fb75..2fbe7b831b 100644
> --- a/hw/9pfs/codir.c
> +++ b/hw/9pfs/codir.c
> @@ -78,6 +78,9 @@ static int do_readdir_many(V9fsPDU *pdu, V9fsFidState *fidp,
>      int len, err = 0;
>      int32_t size = 0;
>      off_t saved_dir_pos;
> +#ifdef CONFIG_WIN32
> +    off_t next_dir_pos;
> +#endif
>      struct dirent *dent;
>      struct V9fsDirEnt *e = NULL;
>      V9fsPath path;
> @@ -124,6 +127,14 @@ static int do_readdir_many(V9fsPDU *pdu, V9fsFidState *fidp,
>              break;
>          }
>  
> +#ifdef CONFIG_WIN32
> +        next_dir_pos = s->ops->telldir(&s->ctx, &fidp->fs);
> +        if (next_dir_pos < 0) {
> +            err = next_dir_pos;
> +            goto out;
> +        }
> +#endif
> +
>          /*
>           * stop this loop as soon as it would exceed the allowed maximum
>           * response message size for the directory entries collected so far,
> @@ -168,7 +179,11 @@ static int do_readdir_many(V9fsPDU *pdu, V9fsFidState *fidp,
>          }
>  
>          size += len;
> +#ifndef CONFIG_WIN32
>          saved_dir_pos = qemu_dirent_off(dent);
> +#else
> +        saved_dir_pos = next_dir_pos;
> +#endif
>      }
>  
>      /* restore (last) saved position */
>