Re: [PATCH 1/3] btrfs-progs: convert/ext2: new debug environment variable to finetune transaction size

[David Sterba <dsterba@suse.cz>]

On Sat, Jan 13, 2024 at 07:15:29PM +1030, Qu Wenruo wrote:
> Since we got a recent bug report about tree-checker triggered for large
> fs conversion, we need a properly way to trigger the problem for test
> case purpose.
> 
> To trigger that bug, we need to meet several conditions:
> 
> - We need to read some tree blocks which has half-backed inodes
> - We need a large enough enough fs to generate more tree blocks than
>   our cache.
> 
>   For our existing test cases, firstly the fs is not that large, thus
>   we may even go just one transaction to generate all the inodes.
> 
>   Secondly we have a global cache for tree blocks, which means a lot of
>   written tree blocks are still in the cache, thus won't trigger
>   tree-checker.
> 
> To make the problem much easier for our existing test case to expose,
> this patch would introduce a debug environment variable:
> BTRFS_PROGS_DEBUG_BLOCKS_USED_THRESHOLD.
> 
> This would affects the threshold for the transaction size, setting it to
> a much smaller value would make the bug much easier to trigger.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  common/utils.c        | 62 +++++++++++++++++++++++++++++++++++++++++++
>  common/utils.h        |  1 +
>  convert/source-ext2.c |  9 ++++++-
>  3 files changed, 71 insertions(+), 1 deletion(-)
> 
> diff --git a/common/utils.c b/common/utils.c
> index 62f0e3f48b39..e6070791f5cc 100644
> --- a/common/utils.c
> +++ b/common/utils.c
> @@ -956,6 +956,68 @@ u8 rand_u8(void)
>  	return (u8)(rand_u32());
>  }
>  
> +/*
> + * Parse a u64 value from an environment variable.
> + *
> + * Supports unit suffixes "KMGTP", the suffix is always 2 ** 10 based.
> + * With proper overflow detection.
> + *
> + * The string must end with '\0', anything unexpected non-suffix string,
> + * including space, would lead to -EINVAL and no value updated.
> + */
> +int get_env_u64(const char *env_name, u64 *value_ret)

There already is a function for parsing sizes parse_size_from_string()
in common/parse-utils.c.