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

[Xiao Guangrong]

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 <address@hidden>
> > ---
> >   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.