Re: [Qemu-devel] [PATCH v6 08/33] exec: allow memory to be allocated from any kind of path

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Oct 30, 2015 at 01:56:02PM +0800, Xiao Guangrong wrote:
> Currently file_ram_alloc() is designed for hugetlbfs, however, the memory
> of nvdimm can come from either raw pmem device eg, /dev/pmem, or the file
> locates at DAX enabled filesystem
> 
> So this patch let it work on any kind of path
> 
> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>

So this allows regular memory to be specified directly.
This needs to be split out and merged separately
from acpi/nvdimm bits.

Alternatively, if it's possible to use nvdimm with DAX fs
(similar to hugetlbfs), leave these patches off for now.


> ---
>  exec.c | 56 +++++++++++++++++---------------------------------------
>  1 file changed, 17 insertions(+), 39 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 8af2570..3ca7e50 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1174,32 +1174,6 @@ void qemu_mutex_unlock_ramlist(void)
>  }
>  
>  #ifdef __linux__
> -
> -#include <sys/vfs.h>
> -
> -#define HUGETLBFS_MAGIC       0x958458f6
> -
> -static long gethugepagesize(const char *path, Error **errp)
> -{
> -    struct statfs fs;
> -    int ret;
> -
> -    do {
> -        ret = statfs(path, &fs);
> -    } while (ret != 0 && errno == EINTR);
> -
> -    if (ret != 0) {
> -        error_setg_errno(errp, errno, "failed to get page size of file %s",
> -                         path);
> -        return 0;
> -    }
> -
> -    if (fs.f_type != HUGETLBFS_MAGIC)
> -        fprintf(stderr, "Warning: path not on HugeTLBFS: %s\n", path);
> -
> -    return fs.f_bsize;
> -}
> -
>  static void *file_ram_alloc(RAMBlock *block,
>                              ram_addr_t memory,
>                              const char *path,
> @@ -1210,20 +1184,24 @@ static void *file_ram_alloc(RAMBlock *block,
>      char *c;
>      void *area;
>      int fd;
> -    uint64_t hpagesize;
> -    Error *local_err = NULL;
> +    uint64_t pagesize;
>  
> -    hpagesize = gethugepagesize(path, &local_err);
> -    if (local_err) {
> -        error_propagate(errp, local_err);
> +    pagesize = qemu_file_get_page_size(path);
> +    if (!pagesize) {
> +        error_setg(errp, "can't get page size for %s", path);
>          goto error;
>      }
> -    block->mr->align = hpagesize;
>  
> -    if (memory < hpagesize) {
> +    if (pagesize == getpagesize()) {
> +        fprintf(stderr, "Memory is not allocated from HugeTlbfs.\n");
> +    }
> +
> +    block->mr->align = pagesize;
> +
> +    if (memory < pagesize) {
>          error_setg(errp, "memory size 0x" RAM_ADDR_FMT " must be equal to "
> -                   "or larger than huge page size 0x%" PRIx64,
> -                   memory, hpagesize);
> +                   "or larger than page size 0x%" PRIx64,
> +                   memory, pagesize);
>          goto error;
>      }
>  
> @@ -1247,14 +1225,14 @@ static void *file_ram_alloc(RAMBlock *block,
>      fd = mkstemp(filename);
>      if (fd < 0) {
>          error_setg_errno(errp, errno,
> -                         "unable to create backing store for hugepages");
> +                         "unable to create backing store for path %s", path);
>          g_free(filename);
>          goto error;
>      }
>      unlink(filename);
>      g_free(filename);

Looks like we are still calling mkstemp/unlink here.
How does this work?

>  
> -    memory = ROUND_UP(memory, hpagesize);
> +    memory = ROUND_UP(memory, pagesize);
>  
>      /*
>       * ftruncate is not supported by hugetlbfs in older
> @@ -1266,10 +1244,10 @@ static void *file_ram_alloc(RAMBlock *block,
>          perror("ftruncate");
>      }
>  
> -    area = qemu_ram_mmap(fd, memory, hpagesize, block->flags & RAM_SHARED);
> +    area = qemu_ram_mmap(fd, memory, pagesize, block->flags & RAM_SHARED);
>      if (area == MAP_FAILED) {
>          error_setg_errno(errp, errno,
> -                         "unable to map backing store for hugepages");
> +                         "unable to map backing store for path %s", path);
>          close(fd);
>          goto error;
>      }
> -- 
> 1.8.3.1