[SeaBIOS] [PATCH v6 4/5] QEMU fw_cfg: Add functions for accessing files by key

[Ben Warren]

> On Feb 20, 2017, at 1:06 PM, Laszlo Ersek <lersek at redhat.com> wrote:
> 
> On 02/20/17 21:14, ben at skyportsystems.com <mailto:ben at skyportsystems.com> wrote:
>> From: Ben Warren <ben at skyportsystems.com>
>> 
>> Due to memory contraints, when resuming from S3 the fw_cfg "files" API
>> isn't available.  This adds a simple API to get a file 'key', and to
>> write to the file using the key as a reference.
>> 
>> Signed-off-by: Ben Warren <ben at skyportsystems.com>
>> ---
>> src/fw/paravirt.c | 32 ++++++++++++++++++++++++++------
>> src/fw/paravirt.h |  2 ++
>> 2 files changed, 28 insertions(+), 6 deletions(-)
>> 
>> diff --git a/src/fw/paravirt.c b/src/fw/paravirt.c
>> index 4618647..225b08b 100644
>> --- a/src/fw/paravirt.c
>> +++ b/src/fw/paravirt.c
>> @@ -329,6 +329,17 @@ qemu_cfg_read_file(struct romfile_s *file, void *dst, u32 maxlen)
>>     return file->size;
>> }
>> 
>> +// Bare-bones function for writing a file knowing only its unique
>> +// identifying key (select)
>> +int
>> +qemu_cfg_write_file_simple(void *src, u16 key, u32 offset, u32 len)
>> +{
>> +    qemu_cfg_select(key);
>> +    qemu_cfg_skip(offset);
>> +    qemu_cfg_write(src, len);
>> +    return len;
>> +}
>> +
>> int
>> qemu_cfg_write_file(void *src, struct romfile_s *file, u32 offset, u32 len)
>> {
>> @@ -339,15 +350,12 @@ qemu_cfg_write_file(void *src, struct romfile_s *file, u32 offset, u32 len)
>>         warn_internalerror();
>>         return -1;
>>     }
>> -    struct qemu_romfile_s *qfile;
>> -    qfile = container_of(file, struct qemu_romfile_s, file);
>> +    u16 key = qemu_get_romfile_key(file);
>>     if (offset == 0) {
>>         /* Do it in one transfer */
>> -        qemu_cfg_write_entry(src, qfile->select, len);
>> +        qemu_cfg_write_entry(src, key, len);
>>     } else {
>> -        qemu_cfg_select(qfile->select);
>> -        qemu_cfg_skip(offset);
>> -        qemu_cfg_write(src, len);
>> +        qemu_cfg_write_file_simple(src, key, offset, len);
>>     }
>>     return len;
>> }
> 
> One of the ideas that I mentioned here was to move not just the second
> branch of the "if" to qemu_cfg_write_file_simple(), but the entire "if"
> -- both branches. Because, qemu_cfg_write_entry() looks suitable for S3
> too, and if that kind of optimization makes sense for normal boot, then
> it makes sense for S3 resume as well.
> 
> Anyway, this is not a functional problem, I won't obsess about it.
> 
> Reviewed-by: Laszlo Ersek <lersek at redhat.com <mailto:lersek at redhat.com>>
> 
Sorry, I misinterpreted your idea.  It makes a lot of sense, so we may as well do it now.  New patch coming.
> Thanks
> Laszlo
> 
> 
—Ben
<snip>
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