Re: [PATCH 4/5] elf2dmp: use Linux mmap with MAP_NORESERVE when possible

[Akihiko Odaki]

On 2023/09/14 7:46, Viktor Prutyanov wrote:
> Glib's g_mapped_file_new maps file with PROT_READ|PROT_WRITE and
> MAP_PRIVATE. This leads to premature physical memory allocation of dump
> file size on Linux hosts and may fail. On Linux, mapping the file with
> MAP_NORESERVE limits the allocation by available memory.
>
> Signed-off-by: Viktor Prutyanov <viktor@daynix.com>
> ---
>   contrib/elf2dmp/qemu_elf.c | 66 +++++++++++++++++++++++++++++++-------
>   contrib/elf2dmp/qemu_elf.h |  4 +++
>   2 files changed, 58 insertions(+), 12 deletions(-)
>
> diff --git a/contrib/elf2dmp/qemu_elf.c b/contrib/elf2dmp/qemu_elf.c
> index ebda60dcb8..94a8c3ad15 100644
> --- a/contrib/elf2dmp/qemu_elf.c
> +++ b/contrib/elf2dmp/qemu_elf.c
> @@ -165,10 +165,37 @@ static bool check_ehdr(QEMU_Elf *qe)
>       return true;
>   }
>   
> -int QEMU_Elf_init(QEMU_Elf *qe, const char *filename)
> +static int QEMU_Elf_map(QEMU_Elf *qe, const char *filename)
>   {
> +#ifdef CONFIG_LINUX

Here CONFIG_LINUX is used while qemu_elf.h uses CONFIG_POSIX.
I also wonder if GLib implementation is really necessary.

> +    struct stat st;
> +
> +    printf("Using Linux's mmap\n");
> +
> +    qe->fd = open(filename, O_RDONLY, 0);
> +    if (qe->fd == -1) {
> +        eprintf("Failed to open ELF dump file \'%s\'\n", filename);
> +        return 1;
> +    }
> +
> +    if (fstat(qe->fd, &st)) {
> +        eprintf("Failed to get size of ELF dump file\n");
> +        close(qe->fd);
> +        return 1;
> +    }
> +    qe->size = st.st_size;
> +
> +    qe->map = mmap(NULL, qe->size, PROT_READ | PROT_WRITE,
> +            MAP_PRIVATE | MAP_NORESERVE, qe->fd, 0);

It should be possible to close the file immediately after mmap().