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exec.c: do not truncate non-empty memory backend file

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For '-object memory-backend-file,mem-path=foo,size=xyz', if the size of
file 'foo' does not match the given size 'xyz', the current QEMU will
truncate the file to the given size, which may corrupt the existing data
in that file. To avoid such data corruption, this patch disables
truncating non-empty backend files.

Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
Message-Id: <20161027042300.5929-2-haozhong.zhang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Haozhong Zhang 2016-10-27 12:22:58 +08:00 committed by Paolo Bonzini
parent f35e44e764
commit d6af99c9f8
1 changed files with 21 additions and 1 deletions
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22
exec.c
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@ -1229,6 +1229,15 @@ void qemu_mutex_unlock_ramlist(void)
}
#ifdef __linux__
static int64_t get_file_size(int fd)
{
int64_t size = lseek(fd, 0, SEEK_END);
if (size < 0) {
return -errno;
}
return size;
}
static void *file_ram_alloc(RAMBlock *block,
ram_addr_t memory,
const char *path,
@ -1240,6 +1249,7 @@ static void *file_ram_alloc(RAMBlock *block,
char *c;
void *area = MAP_FAILED;
int fd = -1;
int64_t file_size;
if (kvm_enabled() && !kvm_has_sync_mmu()) {
error_setg(errp,
@ -1302,6 +1312,8 @@ static void *file_ram_alloc(RAMBlock *block,
}
#endif
file_size = get_file_size(fd);
if (memory < block->page_size) {
error_setg(errp, "memory size 0x" RAM_ADDR_FMT " must be equal to "
"or larger than page size 0x%zx",
@ -1316,8 +1328,16 @@ static void *file_ram_alloc(RAMBlock *block,
* hosts, so don't bother bailing out on errors.
* If anything goes wrong with it under other filesystems,
* mmap will fail.
*
* Do not truncate the non-empty backend file to avoid corrupting
* the existing data in the file. Disabling shrinking is not
* enough. For example, the current vNVDIMM implementation stores
* the guest NVDIMM labels at the end of the backend file. If the
* backend file is later extended, QEMU will not be able to find
* those labels. Therefore, extending the non-empty backend file
* is disabled as well.
*/
if (ftruncate(fd, memory)) {
if (!file_size && ftruncate(fd, memory)) {
perror("ftruncate");
}