Re: [PATCH 1/3] hostmem: Detect and cache fs type for file hostmem

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Apr 18, 2023 at 06:57:47PM -0400, Peter Xu wrote:
> Detect the file system for a memory-backend-file object and cache it within
> the object if possible when CONFIG_LINUX (using statfs).
> 
> Only support the two important types of memory (tmpfs, hugetlbfs) and keep
> the rest as "unknown" for now.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  backends/hostmem-file.c  | 37 ++++++++++++++++++++++++++++++++++++-
>  include/sysemu/hostmem.h |  1 +
>  2 files changed, 37 insertions(+), 1 deletion(-)
> 
> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
> index 25141283c4..2484e45a11 100644
> --- a/backends/hostmem-file.c
> +++ b/backends/hostmem-file.c
> @@ -18,13 +18,17 @@
>  #include "sysemu/hostmem.h"
>  #include "qom/object_interfaces.h"
>  #include "qom/object.h"
> +#ifdef CONFIG_LINUX
> +#include <sys/vfs.h>
> +#include <linux/magic.h>
> +#endif
>  
>  OBJECT_DECLARE_SIMPLE_TYPE(HostMemoryBackendFile, MEMORY_BACKEND_FILE)
>  
>  
>  struct HostMemoryBackendFile {
>      HostMemoryBackend parent_obj;
> -
> +    __fsword_t fs_type;
>      char *mem_path;
>      uint64_t align;
>      bool discard_data;
> @@ -52,6 +56,15 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
>          return;
>      }
>  
> +#ifdef CONFIG_LINUX
> +    struct statfs fs;
> +    if (!statfs(fb->mem_path, &fs)) {
> +        fb->fs_type = fs.f_type;
> +    } else {
> +        fb->fs_type = 0;
> +    }
> +#endif
> +
>      name = host_memory_backend_get_name(backend);
>      ram_flags = backend->share ? RAM_SHARED : 0;
>      ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
> @@ -181,6 +194,28 @@ static void file_backend_unparent(Object *obj)
>      }
>  }
>  
> +const char *file_memory_backend_get_fs_type(Object *obj)
> +{
> +#ifdef CONFIG_LINUX
> +    HostMemoryBackendFile *fb = (HostMemoryBackendFile *)
> +        object_dynamic_cast(obj, TYPE_MEMORY_BACKEND_FILE);
> +
> +    if (!fb) {
> +        goto out;
> +    }
> +
> +    switch (fb->fs_type) {
> +    case TMPFS_MAGIC:
> +        return "tmpfs";
> +    case HUGETLBFS_MAGIC:
> +        return "hugetlbfs";
> +    }
> +
> +out:
> +#endif
> +    return "unknown";
> +}

I rather feel this should be returning an enm, not strings, so
the caller just does a plain equality test rather than string
comparisons


With regards,
Daniel
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