[Libguestfs] [PATCH] make-fs: Don't use du --apparent-size to estimate input size.

[Nikolay Ivanets]

вт, 18 лют. 2020 о 10:48 Richard W.M. Jones <rjones at redhat.com> пише:
>
> When calculating the initial size of the disk we must estimate
> how much space is taken by the input.  This is quite difficult.
>
> For directories we used ‘du --apparent-size -bs DIR’.  This is wrong
> because ’-b’ implies ‘--apparent-size --block-size=1’.  But also
> ‘--apparent-size’ causes du to count the file size rather than number
> of blocks used by files.
>
> If you have a directory containing many small files this usually
> underestimates resulting in disk sizes which are far too small to
> actually contain the files.
>
> There's no really good answer here because du can't exactly do what we
> want, but we can at least remove this flag.  This causes much larger
> estimates and therefore much larger virtual disks.
>
> Thanks: Nikolay Ivanets
> ---
>  make-fs/make-fs.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/make-fs/make-fs.c b/make-fs/make-fs.c
> index 5d8c3a385..386142280 100644
> --- a/make-fs/make-fs.c
> +++ b/make-fs/make-fs.c
> @@ -393,7 +393,7 @@ static int
>  estimate_input (const char *input, uint64_t *estimate_rtn, char **ifmt_rtn)
>  {
>    struct stat statbuf;
> -  const char *argv[6];
> +  const char *argv[5];
>    CLEANUP_UNLINK_FREE char *tmpfile = NULL;
>    CLEANUP_FCLOSE FILE *fp = NULL;
>    char line[256];
> @@ -424,11 +424,10 @@ estimate_input (const char *input, uint64_t *estimate_rtn, char **ifmt_rtn)
>      }
>
>      argv[0] = "du";
> -    argv[1] = "--apparent-size";
> -    argv[2] = "-b";
> -    argv[3] = "-s";
> -    argv[4] = input;
> -    argv[5] = NULL;
> +    argv[1] = "--block-size=1";
> +    argv[2] = "-s";
> +    argv[3] = input;
> +    argv[4] = NULL;
>
>      if (exec_command ((char **) argv, tmpfile) == -1)
>        return -1;
> --
> 2.24.1
>

That didn't help either. And with sparse files even made things worse:
holes are not taken into account now at all.

I repeat my thoughts here again: it is all like "cats and rats game".
We cannot properly handle all the possible cases.
I think we can agree that virt-make-fs MAY fail and it is expected
situation.  Just let the user know that he need to adjust size
manually.

--
    Mykola Ivanets