Commit d6af99c9 authored by Haozhong Zhang's avatar Haozhong Zhang Committed by Paolo Bonzini
Browse files

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



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: default avatarHaozhong Zhang <haozhong.zhang@intel.com>
Message-Id: <20161027042300.5929-2-haozhong.zhang@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent f35e44e7

exec.c

+21 −1
Original line number Diff line number Diff line
@@ -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");

    }