memory: fetch pmem size in get_file_size()
Neither stat(2) nor lseek(2) report the size of Linux devdax pmem
character device nodes. Commit 314aec4a6e06844937f1677f6cba21981005f389
("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>
diff --git a/exec.c b/exec.c
index b9511be..8b99897 100644
--- a/exec.c
+++ b/exec.c
@@ -1791,7 +1791,39 @@
#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;
}
