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memory: fetch pmem size in get_file_size()

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Neither stat(2) nor lseek(2) report the size of Linux devdax pmem
character device nodes.  Commit 314aec4a6e
("hostmem-file: reject invalid pmem file sizes") added code to
hostmem-file.c to fetch the size from sysfs and compare against the
user-provided size=NUM parameter:

  if (backend->size > size) {
      error_setg(errp, "size property %" PRIu64 " is larger than "
                 "pmem file \"%s\" size %" PRIu64, backend->size,
                 fb->mem_path, size);
      return;
  }

It turns out that exec.c:qemu_ram_alloc_from_fd() already has an
equivalent size check but it skips devdax pmem character devices because
lseek(2) returns 0:

  if (file_size > 0 && file_size < size) {
      error_setg(errp, "backing store %s size 0x%" PRIx64
                 " does not match 'size' option 0x" RAM_ADDR_FMT,
                 mem_path, file_size, size);
      return NULL;
  }

This patch moves the devdax pmem file size code into get_file_size() so
that we check the memory size in a single place:
qemu_ram_alloc_from_fd().  This simplifies the code and makes it more
general.

This also fixes the problem that hostmem-file only checks the devdax
pmem file size when the pmem=on parameter is given.  An unchecked
size=NUM parameter can lead to SIGBUS in QEMU so we must always fetch
the file size for Linux devdax pmem character device nodes.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20190830093056.12572-1-stefanha@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2019-08-30 10:30:56 +01:00 • committed by Paolo Bonzini
parent 41a2635124
commit 72d41eb4b8
5 changed files with 33 additions and 96 deletions
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34
exec.c
View file

@ -1791,7 +1791,39 @@ long qemu_maxrampagesize(void)
#ifdef CONFIG_POSIX
static int64_t get_file_size(int fd)
{
int64_t size = lseek(fd, 0, SEEK_END);
int64_t size;
#if defined(__linux__)
struct stat st;
if (fstat(fd, &st) < 0) {
return -errno;
}
/* Special handling for devdax character devices */
if (S_ISCHR(st.st_mode)) {
g_autofree char *subsystem_path = NULL;
g_autofree char *subsystem = NULL;
subsystem_path = g_strdup_printf("/sys/dev/char/%d:%d/subsystem",
major(st.st_rdev), minor(st.st_rdev));
subsystem = g_file_read_link(subsystem_path, NULL);
if (subsystem && g_str_has_suffix(subsystem, "/dax")) {
g_autofree char *size_path = NULL;
g_autofree char *size_str = NULL;
size_path = g_strdup_printf("/sys/dev/char/%d:%d/size",
major(st.st_rdev), minor(st.st_rdev));
if (g_file_get_contents(size_path, &size_str, NULL, NULL)) {
return g_ascii_strtoll(size_str, NULL, 0);
}
}
}
#endif /* defined(__linux__) */
/* st.st_size may be zero for special files yet lseek(2) works */
size = lseek(fd, 0, SEEK_END);
if (size < 0) {
return -errno;
}