[4/5] core/nvram: add support for skiboot config strings

This allows the ibm,skiboot partition to be used to store NUL terminated
key=value OF configuration strings. These strings can be written using
the nvram utility found in the linux powerpc-utils package. Currently
the only use case for this is passing command line arguments to the
boot kernel so only ASCII strings are supported. The 0xFF binary
escaping mechanism for configuration strings is not supported.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
---
 core/nvram-format.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++----
 include/nvram.h     |  2 ++
 2 files changed, 64 insertions(+), 5 deletions(-)

On Mon, Aug 8, 2016 at 12:28 PM, Oliver O'Halloran <oohall@gmail.com> wrote:
> This allows the ibm,skiboot partition to be used to store NUL terminated
> key=value OF configuration strings. These strings can be written using
> the nvram utility found in the linux powerpc-utils package. Currently
> the only use case for this is passing command line arguments to the
> boot kernel so only ASCII strings are supported. The 0xFF binary
> escaping mechanism for configuration strings is not supported.
>
> Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
> ---
>  core/nvram-format.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++----
>  include/nvram.h     |  2 ++
>  2 files changed, 64 insertions(+), 5 deletions(-)
>
> diff --git a/core/nvram-format.c b/core/nvram-format.c
> index be8d77f8394b..57d51842e360 100644
> --- a/core/nvram-format.c
> +++ b/core/nvram-format.c
> @@ -28,6 +28,8 @@ struct chrp_nvram_hdr {
>         char            name[12];
>  };
>
> +struct chrp_nvram_hdr *skiboot_part_hdr;
> +
>  #define NVRAM_SIG_FW_PRIV      0x51
>  #define NVRAM_SIG_SYSTEM       0x70
>  #define NVRAM_SIG_FREE         0x7f
> @@ -115,7 +117,8 @@ int nvram_check(void *nvram_image, const uint32_t nvram_size)
>  {
>         unsigned int offset = 0;
>         bool found_common = false;
> -       bool found_skiboot = false;
> +
> +       skiboot_part_hdr = NULL;
>
>         while (offset + sizeof(struct chrp_nvram_hdr) < nvram_size) {
>                 struct chrp_nvram_hdr *h = nvram_image + offset;
> @@ -138,7 +141,7 @@ int nvram_check(void *nvram_image, const uint32_t nvram_size)
>
>                 if (h->sig == NVRAM_SIG_FW_PRIV &&
>                     strcmp(h->name, NVRAM_NAME_FW_PRIV) == 0)
> -                       found_skiboot = true;
> +                       skiboot_part_hdr = h;
>
>                 offset += h->len << 4;
>                 if (offset > nvram_size) {
> @@ -151,9 +154,9 @@ int nvram_check(void *nvram_image, const uint32_t nvram_size)
>                 prerror("NVRAM: Common partition not found !\n");
>                 goto failed;
>         }
> -       if (!found_skiboot) {
> -               prerror("NVRAM: Skiboot private partition "
> -                       "not found !\n");
> +
> +       if (!skiboot_part_hdr) {
> +               prerror("NVRAM: Skiboot private partition not found !\n");
>                 goto failed;
>         } else {
>                 /*
> @@ -176,3 +179,57 @@ int nvram_check(void *nvram_image, const uint32_t nvram_size)
>   failed:
>         return -1;
>  }
> +
> +static const char *find_next_key(const char *start, const char *end)
> +{
> +       while (start < end) {
> +               if (*start == 0)
> +                       return start + 1;
> +
> +               start++;
> +       }
> +
> +       return end;
> +}
> +
> +/*
> + * nvram_query() - Returns the value associated with a key. The ibm,skiboot
> + * partition contains a set of key=value pairs separated by NUL terminators.
> + */
> +const void *nvram_query(const char *key, size_t *length)
> +{
> +       const char *part_end = (const void *) skiboot_part_hdr +

Why not const char *?

> +               skiboot_part_hdr->len * 16;
> +       const char *start = (void *)skiboot_part_hdr +

Same.

> +               sizeof(*skiboot_part_hdr);
> +       const char *end = find_next_key(start, part_end);
> +       int key_len = strlen(key);

Is there a maximum length for a key?

> +
> +       prlog(PR_TRACE, "start: %p %s\n", start, start);
> +       prlog(PR_TRACE, "end:   %p %s\n", end, end);

No NVRAM prefix?

> +
> +       while (start < end) {
> +               int remaining = part_end - start;
> +
> +               if (key_len + 1 > remaining)
> +                       return NULL;
> +
> +               if (strlen(start))

Maximum length?

> +                       prlog(PR_TRACE, "NVRAM: '%s' (%lu)\n",
> +                               start, strlen(start));

You're relying on strncmp returning false for the empty key to skip
the next bit?

Would a goto make your intention clearer?

> +
> +               if (!strncmp(key, start, key_len) && start[key_len] == '=') {
> +                       const char *value = &start[key_len + 1];
> +
> +                       if (length)
> +                               *length = end - value;
> +
> +                       return value;
> +               }
> +
> +               start = end;
> +               end = find_next_key(end, part_end);
> +       }
> +
> +       return NULL;
> +}
> diff --git a/include/nvram.h b/include/nvram.h
> index c90c5712a2f7..b4faa2e72dc8 100644
> --- a/include/nvram.h
> +++ b/include/nvram.h
> @@ -21,4 +21,6 @@ int nvram_format(void *nvram_image, uint32_t nvram_size);
>  int nvram_check(void *nvram_image, uint32_t nvram_size);
>  void nvram_reinit(void);
>
> +const void *nvram_query(const char *name, size_t *length);
> +
>  #endif /* __NVRAM_H */
> --
> 2.5.5
>
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