Re: [Qemu-block] [Qemu-devel] [PATCH v2] blockdev: clean up error handling in do_open_tray

[Markus Armbruster]

Colin Lord <address@hidden> writes:

> Returns negative error codes and accompanying error messages in cases where
> the device has no tray or the tray is locked and isn't forced open. This
> extra information should result in better flexibility in functions that
> call do_open_tray.
>
> Signed-off-by: Colin Lord <address@hidden>
> ---
> v2: fix function documentation, improve commit wording, and remove
> unnecessary null check
>  blockdev.c | 36 +++++++++++++++++++++---------------
>  1 file changed, 21 insertions(+), 15 deletions(-)
>
> diff --git a/blockdev.c b/blockdev.c
> index 717785e..d50a2a5 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -2286,17 +2286,14 @@ void qmp_eject(const char *device, bool has_force, 
> bool force, Error **errp)
>      }
>  
>      rc = do_open_tray(device, force, &local_err);
> -    if (local_err) {
> +    if (rc == -ENOSYS) {
> +        error_free(local_err);
> +        local_err = NULL;
> +    } else if (local_err) {
>          error_propagate(errp, local_err);
>          return;
>      }

I like to put the error case in a conditional, and leave the normal flow
unindented, because it makes the normal flow easier to follow:

       if (rc && rc != -ENOSYS) {
           error_propagate(errp, local_err);
           return;
       }
       error_free(local_err);

error_free(NULL) is safe.

>  
> -    if (rc == EINPROGRESS) {
> -        error_setg(errp, "Device '%s' is locked and force was not specified, 
> "
> -                   "wait for tray to open and try again", device);
> -        return;
> -    }
> -
>      qmp_x_blockdev_remove_medium(device, errp);
>  }
>  
> @@ -2325,10 +2322,9 @@ void qmp_block_passwd(bool has_device, const char 
> *device,
>  }
>  
>  /**
> - * returns -errno on fatal error, +errno for non-fatal situations.
> - * errp will always be set when the return code is negative.
> - * May return +ENOSYS if the device has no tray,
> - * or +EINPROGRESS if the tray is locked and the guest has been notified.
> + * returns -errno on all errors, and errp will be set on error
> + * May return the non-fatal error codes -ENOSYS if the device has no tray,
> + * or -EINPROGRESS if the tray is locked and the guest has been notified.
>   */

What does the function do?

What does it return on success?

Suggest imperative mood.

Here's my try:

   /*
    * Attempt to open the tray of @device.
    * If @force, ignore its tray lock.
    * Else, if the tray is locked, don't open it, but ask the guest to
    * open it.
    * On error, store an error through @errp and return -errno.
    * If @device does not exist, return -ENODEV.
    * If it has no removable media, return -ENOTSUP.
    * If it has no tray, return -ENOSYS.
    * If the guest was asked to open the tray, return -EINPROGRESS.
    * Else, return 0.
    */

>  static int do_open_tray(const char *device, bool force, Error **errp)
>  {
> @@ -2348,8 +2344,8 @@ static int do_open_tray(const char *device, bool force, 
> Error **errp)
>      }
>  
>      if (!blk_dev_has_tray(blk)) {
> -        /* Ignore this command on tray-less devices */
> -        return ENOSYS;
> +        error_setg(errp, "Device '%s' does not have a tray", device);
> +        return -ENOSYS;
>      }
>  
>      if (blk_dev_is_tray_open(blk)) {
> @@ -2366,7 +2362,9 @@ static int do_open_tray(const char *device, bool force, 
> Error **errp)
>      }
>  
>      if (locked && !force) {
> -        return EINPROGRESS;
> +        error_setg(errp, "Device '%s' is locked and force was not specified, 
> "
> +                   "wait for tray to open and try again", device);
> +        return -EINPROGRESS;
>      }
>  
>      return 0;
> @@ -2375,10 +2373,18 @@ static int do_open_tray(const char *device, bool 
> force, Error **errp)
>  void qmp_blockdev_open_tray(const char *device, bool has_force, bool force,
>                              Error **errp)
>  {
> +    Error *local_err = NULL;
> +    int rc;
> +
>      if (!has_force) {
>          force = false;
>      }
> -    do_open_tray(device, force, errp);
> +    rc = do_open_tray(device, force, &local_err);
> +    if (rc == -EINPROGRESS || rc == -ENOSYS) {
> +        error_free(local_err);
> +    } else {
> +        error_propagate(errp, local_err);
> +    }
>  }

Likewise:

       if (rc && rc != -ENOSYS && rc != EINPROGRESS) {
           error_propagate(errp, local_err);
           return;
       }
       error_free(local_err);

>  
>  void qmp_blockdev_close_tray(const char *device, Error **errp)

While you're cleaning up: mind moving the forward declaration of
do_open_tray() to the beginning?