Re: [Qemu-devel] [PATCH v6 09/33] exec: allow file_ram_alloc to work on file

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

On 10/30/2015 10:25 PM, Vladimir Sementsov-Ogievskiy wrote:
> On 30.10.2015 08:56, Xiao Guangrong wrote:
>> Currently, file_ram_alloc() only works on directory - it creates a file
>> under @path and do mmap on it
>>
>> This patch tries to allow it to work on file directly, if @path is a
>> directory it works as before, otherwise it treats @path as the target
>> file then directly allocate memory from it
>>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>> ---
>>   exec.c | 80 ++++++++++++++++++++++++++++++++++++++++++------------------------
>>   1 file changed, 51 insertions(+), 29 deletions(-)
>>
>> diff --git a/exec.c b/exec.c
>> index 3ca7e50..f219010 100644
>> --- a/exec.c
>> +++ b/exec.c
>> @@ -1174,14 +1174,60 @@ void qemu_mutex_unlock_ramlist(void)
>>   }
>>   #ifdef __linux__
>> +static bool path_is_dir(const char *path)
>> +{
>> +    struct stat fs;
>> +
>> +    return stat(path, &fs) == 0 && S_ISDIR(fs.st_mode);
>> +}
>> +
>> +static int open_file_path(RAMBlock *block, const char *path, size_t size)
>
> I think the name should be more descriptive, as it is very special function in common exec.c and it
> doesn't "just open file path'.. May be open_ram_file_path

Okay, good to me. :)

>
>
>> +{
>> +    char *filename;
>> +    char *sanitized_name;
>> +    char *c;
>> +    int fd;
>> +
>> +    if (!path_is_dir(path)) {
>> +        int flags = (block->flags & RAM_SHARED) ? O_RDWR : O_RDONLY;
>> +
>> +        flags |= O_EXCL;
>> +        return open(path, flags);
>> +    }
>
> Was not there old scenarios when path is file? statfs will  success for any file withing mounted
> filesystem.
>

Yes.

The old scenarios will create a temporary file under the @path that stop regular file's work.


> Also, may be we shouldn't warn about "Memory is not allocated from HugeTlbfs.\n" in case of
> !path_is_dir ?
>

A file from hugetlbfs and attach it as backend memory is a valid case to users.