Re: [Qemu-block] [Qemu-devel] [PATCH for-2.10 07/16] block/file-posix: Generalize raw_regular_truncate

[Max Reitz]

On 20.03.2017 12:00, Stefan Hajnoczi wrote:
> On Mon, Mar 13, 2017 at 10:40:36PM +0100, Max Reitz wrote:
>> Currently, raw_regular_truncate() is intended for setting the size of a
>> newly created file. However, we also want to use it for truncating an
>> existing file in which case only the newly added space (when growing)
>> should be preallocated.
>>
>> This also means that if resizing failed, we should try to restore the
>> original file size. This is important when using preallocation.
>>
>> Signed-off-by: Max Reitz <address@hidden>
>> ---
>>  block/file-posix.c | 73 
>> ++++++++++++++++++++++++++++++++++++++++++++----------
>>  1 file changed, 60 insertions(+), 13 deletions(-)
>>
>> diff --git a/block/file-posix.c b/block/file-posix.c
>> index 35a9e43f3e..cd229324ba 100644
>> --- a/block/file-posix.c
>> +++ b/block/file-posix.c
>> @@ -1384,11 +1384,39 @@ static void raw_close(BlockDriverState *bs)
>>      }
>>  }
>>  
>> -static int raw_regular_truncate(int fd, int64_t offset, PreallocMode 
>> prealloc,
>> +/**
>> + * Truncates the given regular file @fd to @offset and, when growing, fills 
>> the
>> + * new space according to @prealloc.
>> + *
>> + * @create must be true iff the file is new. In that case, @bs is ignored. 
>> If
>> + * @create is false, @bs must be valid and correspond to the same file as 
>> @fd.
> 
> Returns: 0 on success, -errno on failure.

Yep, will add.

>> + */
>> +static int raw_regular_truncate(int fd, BlockDriverState *bs, int64_t 
>> offset,
> 
> The presence of both a file descriptor and a BlockDriverState (actually
> it must be a BDRVRawState) arguments is unusual.  It seems bs is needed
> for bdrv_getlength().
> 
> How about using fstat(fd, &st) and then dropping bs and create?

Well, I could do that, but bdrv_getlength() is a bit simpler and I don't
see much of an issue with specifying both an fd and a bs.

>> +                                PreallocMode prealloc, bool create,
>>                                  Error **errp)
>>  {
>>      int result = 0;
>> -    char *buf;
>> +    int64_t current_length = 0;
>> +    char *buf = NULL;
>> +
>> +    assert(create || bs);
>> +    if (!create) {
>> +        BDRVRawState *s = bs->opaque;
>> +        assert(s->fd == fd);
>> +    }
>> +
>> +    if (!create) {
>> +        current_length = bdrv_getlength(bs);
>> +        if (current_length < 0) {
>> +            error_setg_errno(errp, -current_length,
>> +                             "Could not inquire current length");
>> +            return -current_length;
>> +        }
>> +
>> +        if (current_length > offset && prealloc != PREALLOC_MODE_OFF) {
>> +            return -ENOTSUP;
>> +        }
> 
> Missing error_setg().

Indeed! Will fix.

Max

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