Re: [Qemu-block] [PATCH v2] file-posix: specify expected filetypes

[John Snow]

On 01/17/2018 05:45 AM, Kevin Wolf wrote:
> Am 15.01.2018 um 23:50 hat John Snow geschrieben:
>> I don't think there's a legitimate reason to open directories as if
>> they were files. This prevents QEMU from opening and attempting to probe
>> a directory inode, which can break in exciting ways. One of those ways
>> is lseek on ext4/xfs, which will return 0x7fffffffffffffff as the file
>> size instead of EISDIR. This can coax QEMU into responding with a
>> confusing "file too big" instead of "Hey, that's not a file".
>>
>> See: https://bugs.launchpad.net/qemu/+bug/1739304/
>> Signed-off-by: John Snow <address@hidden>
>> ---
>>
>> v2: Is something like this what you had in mind, Kevin?
>>     I couldn't make the hdev/cdrom checks more specific
>>     as I'm not sure which environments expect which, but
>>     if you know I can tighten it.
> 
> This should do. We could in theory be more specific about which OS
> expects block devices and which one uses character devices, but there's
> probably no point in doing that. And without further research I couldn't
> say much more than that Linux uses block devices and FreeBSD character
> devices.
> 

The risk of breaking something stupid seems worse than the benefit of
tightening this.

(Also I don't want to install Solaris.)

>>  block/file-posix.c | 38 +++++++++++++++++++++++++++++---------
>>  1 file changed, 29 insertions(+), 9 deletions(-)
> 
> As Eric said, it would be good to add a deprecation note to
> qemu-doc.texi (and probably also the changelog in the wiki).
> 

Yeah, sure thing.

>> diff --git a/block/file-posix.c b/block/file-posix.c
>> index 36ee89e940..fe06cdb8f8 100644
>> --- a/block/file-posix.c
>> +++ b/block/file-posix.c
>> @@ -417,7 +417,8 @@ static QemuOptsList raw_runtime_opts = {
>>  };
>>  
>>  static int raw_open_common(BlockDriverState *bs, QDict *options,
>> -                           int bdrv_flags, int open_flags, Error **errp)
>> +                           int bdrv_flags, int open_flags,
>> +                           bool device, Error **errp)
>>  {
>>      BDRVRawState *s = bs->opaque;
>>      QemuOpts *opts;
>> @@ -556,10 +557,30 @@ static int raw_open_common(BlockDriverState *bs, QDict 
>> *options,
>>          error_setg_errno(errp, errno, "Could not stat file");
>>          goto fail;
>>      }
>> -    if (S_ISREG(st.st_mode)) {
>> -        s->discard_zeroes = true;
>> -        s->has_fallocate = true;
>> +
>> +    if (!device) {
>> +        if (S_ISBLK(st.st_mode)) {
>> +            warn_report("Opening a block device as file using 'file'"
>> +                        "driver is deprecated");
> 
> All your line-wrapped strings are missing a space at the end of the
> first line.
> 
> Kevin
> 

Oh, duh.