On 03/11/2015 04:56, Xiao Guangrong wrote:
>
>
> On 11/03/2015 05:12 AM, Paolo Bonzini wrote:
>>
>>
>> On 02/11/2015 10:13, Xiao Guangrong wrote:
>>> Currently, file_ram_alloc() only works on directory - it creates a file
>>> under @path and do mmap on it
>>>
>>> This patch tries to allow it to work on file directly, if @path is a
>>> directory it works as before, otherwise it treats @path as the target
>>> file then directly allocate memory from it
>>>
>>> Signed-off-by: Xiao Guangrong <guangrong.x...@linux.intel.com>
>>> ---
>>> exec.c | 80
>>> ++++++++++++++++++++++++++++++++++++++++++------------------------
>>> 1 file changed, 51 insertions(+), 29 deletions(-)
>>>
>>> diff --git a/exec.c b/exec.c
>>> index 9075f4d..db0fdaf 100644
>>> --- a/exec.c
>>> +++ b/exec.c
>>> @@ -1174,14 +1174,60 @@ void qemu_mutex_unlock_ramlist(void)
>>> }
>>>
>>> #ifdef __linux__
>>> +static bool path_is_dir(const char *path)
>>> +{
>>> + struct stat fs;
>>> +
>>> + return stat(path, &fs) == 0 && S_ISDIR(fs.st_mode);
>>> +}
>>> +
>>> +static int open_ram_file_path(RAMBlock *block, const char *path,
>>> size_t size)
>>> +{
>>> + char *filename;
>>> + char *sanitized_name;
>>> + char *c;
>>> + int fd;
>>> +
>>> + if (!path_is_dir(path)) {
>>> + int flags = (block->flags & RAM_SHARED) ? O_RDWR : O_RDONLY;
>>> +
>>> + flags |= O_EXCL;
>>> + return open(path, flags);
>>> + }
>>> +
>>> + /* Make name safe to use with mkstemp by replacing '/' with '_'. */
>>> + sanitized_name = g_strdup(memory_region_name(block->mr));
>>> + for (c = sanitized_name; *c != '\0'; c++) {
>>> + if (*c == '/') {
>>> + *c = '_';
>>> + }
>>> + }
>>> + filename = g_strdup_printf("%s/qemu_back_mem.%s.XXXXXX", path,
>>> + sanitized_name);
>>> + g_free(sanitized_name);
>>> + fd = mkstemp(filename);
>>> + if (fd >= 0) {
>>> + unlink(filename);
>>> + /*
>>> + * ftruncate is not supported by hugetlbfs in older
>>> + * hosts, so don't bother bailing out on errors.
>>> + * If anything goes wrong with it under other filesystems,
>>> + * mmap will fail.
>>> + */
>>> + if (ftruncate(fd, size)) {
>>> + perror("ftruncate");
>>> + }
>>> + }
>>> + g_free(filename);
>>> +
>>> + return fd;
>>> +}
>>> +
>>> static void *file_ram_alloc(RAMBlock *block,
>>> ram_addr_t memory,
>>> const char *path,
>>> Error **errp)
>>> {
>>> - char *filename;
>>> - char *sanitized_name;
>>> - char *c;
>>> void *area;
>>> int fd;
>>> uint64_t pagesize;
>>> @@ -1212,38 +1258,14 @@ static void *file_ram_alloc(RAMBlock *block,
>>> goto error;
>>> }
>>>
>>> - /* Make name safe to use with mkstemp by replacing '/' with '_'. */
>>> - sanitized_name = g_strdup(memory_region_name(block->mr));
>>> - for (c = sanitized_name; *c != '\0'; c++) {
>>> - if (*c == '/')
>>> - *c = '_';
>>> - }
>>> -
>>> - filename = g_strdup_printf("%s/qemu_back_mem.%s.XXXXXX", path,
>>> - sanitized_name);
>>> - g_free(sanitized_name);
>>> + memory = ROUND_UP(memory, pagesize);
>>>
>>> - fd = mkstemp(filename);
>>> + fd = open_ram_file_path(block, path, memory);
>>> if (fd < 0) {
>>> error_setg_errno(errp, errno,
>>> "unable to create backing store for path
>>> %s", path);
>>> - g_free(filename);
>>> goto error;
>>> }
>>> - unlink(filename);
>>> - g_free(filename);
>>> -
>>> - memory = ROUND_UP(memory, pagesize);
>>> -
>>> - /*
>>> - * ftruncate is not supported by hugetlbfs in older
>>> - * hosts, so don't bother bailing out on errors.
>>> - * If anything goes wrong with it under other filesystems,
>>> - * mmap will fail.
>>> - */
>>> - if (ftruncate(fd, memory)) {
>>> - perror("ftruncate");
>>> - }
>>>
>>> area = qemu_ram_mmap(fd, memory, pagesize, block->flags &
>>> RAM_SHARED);
>>> if (area == MAP_FAILED) {
>>>
>>
>> I was going to send tomorrow a pull request for a similar patch,
>> "backends/hostmem-file: Allow to specify full pathname for backing file".
>>
>> The main difference seems to be your usage of O_EXCL. Can you explain
>> why you added it?
>
> It' used if we pass a block device as a NVDIMM backend memory:
> O_EXCL can be used without O_CREAT if pathname refers to a block
> device. If the block device
> is in use by the system (e.g., mounted), open() fails with the error EBUSY
That makes sense, but I think it's better to be consistent with the
handling of block devices. Block devices do not use O_EXCL when QEMU
opens them; I guess in principle it would also be possible to share a
single pmem backend between multiple guests.
Paolo
