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 <vik...@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().