Re: [Qemu-block] [PATCH v3 1/3] block: introducing 'bdrv_co_delete_file' interface

[John Snow]

It looks like this one has gone un-noticed for a little while.

On 3/26/19 5:17 PM, Daniel Henrique Barboza wrote:
> Adding to Block Drivers the capability of being able to clean up
> its created files can be useful in certain situations. For the
> LUKS driver, for instance, a failure in one of its authentication
> steps can leave files in the host that weren't there before.
> 
> This patch adds the 'bdrv_co_delete_file' interface to block
> drivers and add it to the 'file' driver in file-posix.c. The
> implementation is given by 'raw_co_delete_file'. The helper
> 'bdrv_path_is_regular_file' is being used only in raw_co_delete_file
> at this moment, but it will be used inside LUKS in a later patch.
> Foreseeing this future use, let's put it in block.c and make it
> public.
> 
> Suggested-by: Daniel P. Berrangé <address@hidden>
> Signed-off-by: Daniel Henrique Barboza <address@hidden>
> ---
>  block.c                   | 11 +++++++++++
>  block/file-posix.c        | 28 ++++++++++++++++++++++++++++
>  include/block/block.h     |  1 +
>  include/block/block_int.h |  6 ++++++
>  4 files changed, 46 insertions(+)
> 
> diff --git a/block.c b/block.c
> index 0a93ee9ac8..227362b282 100644
> --- a/block.c
> +++ b/block.c
> @@ -621,6 +621,17 @@ int get_tmp_filename(char *filename, int size)
>  #endif
>  }
>  
> +/**
> + * Helper that checks if a given string represents a regular
> + * local file.
> + */
> +bool bdrv_path_is_regular_file(const char *path)
> +{
> +    struct stat st;
> +
> +    return (stat(path, &st) == 0) && S_ISREG(st.st_mode);
> +}
> +
>  /*
>   * Detect host devices. By convention, /dev/cdrom[N] is always
>   * recognized as a host CDROM.
> diff --git a/block/file-posix.c b/block/file-posix.c
> index d102f3b222..09d84bab37 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -2342,6 +2342,33 @@ static int coroutine_fn raw_co_create_opts(const char 
> *filename, QemuOpts *opts,
>      return raw_co_create(&options, errp);
>  }
>  
> +/**
> + * Co-routine function that erases a regular file.
> + */
> +static int coroutine_fn raw_co_delete_file(const char *filename,
> +                                           Error **errp)

Do we need to mark functions that make no use of coroutines as
coroutine_fn? I guess this way the interface is *allowed* to be a
coroutine if other drivers need to make use of that.

> +{
> +    int ret;
> +
> +    /* Skip file: protocol prefix */
> +    strstart(filename, "file:", &filename);
> +

This sticks out as fragile to me, but I guess that's exactly how create
works, so... OK.

> +    if (!bdrv_path_is_regular_file(filename)) {
> +        ret = -ENOENT;
> +        error_setg_errno(errp, -ret, "%s is not a regular file", filename);
> +        goto done;
> +    }
> +
> +    ret = unlink(filename);
> +    if (ret < 0) {
> +        ret = -errno;
> +        error_setg_errno(errp, -ret, "Error when deleting file %s", 
> filename);
> +    }
> +
> +done:
> +    return ret;
> +}
> +
>  /*
>   * Find allocation range in @bs around offset @start.
>   * May change underlying file descriptor's file offset.
> @@ -2867,6 +2894,7 @@ BlockDriver bdrv_file = {
>      .bdrv_co_block_status = raw_co_block_status,
>      .bdrv_co_invalidate_cache = raw_co_invalidate_cache,
>      .bdrv_co_pwrite_zeroes = raw_co_pwrite_zeroes,
> +    .bdrv_co_delete_file = raw_co_delete_file,
>  
>      .bdrv_co_preadv         = raw_co_preadv,
>      .bdrv_co_pwritev        = raw_co_pwritev,
> diff --git a/include/block/block.h b/include/block/block.h
> index e452988b66..820643f96d 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -363,6 +363,7 @@ int bdrv_freeze_backing_chain(BlockDriverState *bs, 
> BlockDriverState *base,
>                                Error **errp);
>  void bdrv_unfreeze_backing_chain(BlockDriverState *bs, BlockDriverState 
> *base);
>  
> +bool bdrv_path_is_regular_file(const char *path);
>  
>  typedef struct BdrvCheckResult {
>      int corruptions;
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 01e855a066..74abb78ce7 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -309,6 +309,12 @@ struct BlockDriver {
>       */
>      int coroutine_fn (*bdrv_co_flush)(BlockDriverState *bs);
>  
> +    /*
> +     * Delete a local created file.
> +     */
> +    int coroutine_fn (*bdrv_co_delete_file)(const char *filename,
> +                                            Error **errp);
> +
>      /*
>       * Flushes all data that was already written to the OS all the way down 
> to
>       * the disk (for example file-posix.c calls fsync()).
> 

Seems alright at a glance, if we want this interface.

Kevin, do we?

--js