[Qemu-devel] Re: [PATCH v2 2/4] Clean-up a little bit the RW related bits of BDRV_O_FLAGS. BDRV_O_RDONLY gone (and so is BDRV_O_ACCESS). Default value for bdrv_flags (0/zero) is READ-ONLY. Need to explicitly request READ-WRITE.

[Naphtali Sprei]

Michael S. Tsirkin wrote:
> On Sun, Jan 17, 2010 at 04:48:13PM +0200, Naphtali Sprei wrote:
>> Instead of using the field 'readonly' of the BlockDriverState struct for 
>> passing the request,
>> pass the request in the flags parameter to the function.
>>
>> Signed-off-by: Naphtali Sprei <address@hidden>
> 
> Many changes seem to be about passing 0 to bdrv_open. This is not what
> the changelog says the patch does. Better split unrelated changes to a
> separate patch.

Thanks for the review.

Unfortunately, some of my comments went to the subject and are not part of the 
changelog.
So here's the (intended) changelog. This will clear-up some of your comments.

Clean-up a little bit the RW related bits of BDRV_O_FLAGS.
BDRV_O_RDONLY gone (and so is BDRV_O_ACCESS).
Default value for bdrv_flags (0/zero) is READ-ONLY. Need to explicitly request 
READ-WRITE.
Instead of using the field 'readonly' of the BlockDriverState struct for 
passing the request,
pass the request in the flags parameter to the function.



> 
> One of the things you seem to do is get rid of BDRV_O_RDONLY.  Why is
> this an improvement? Symbolic name like BDRV_O_RDONLY seems better than
> 0.

See Markus reply (thanks Markus).

> 
>> ---
>>  block.c           |   31 +++++++++++++++++--------------
>>  block.h           |    2 --
>>  block/raw-posix.c |    2 +-
>>  block/raw-win32.c |    4 ++--
>>  block/vmdk.c      |    9 +++++----
>>  hw/xen_disk.c     |    2 +-
>>  monitor.c         |    2 +-
>>  qemu-img.c        |   10 ++++++----
>>  qemu-io.c         |   14 ++++++--------
>>  qemu-nbd.c        |    2 +-
>>  vl.c              |    8 ++++----
>>  11 files changed, 44 insertions(+), 42 deletions(-)
>>
>> diff --git a/block.c b/block.c
>> index 115e591..8def3c4 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -310,7 +310,7 @@ static BlockDriver *find_image_format(const char 
>> *filename)
>>      if (drv && strcmp(drv->format_name, "vvfat") == 0)
>>          return drv;
>>  
>> -    ret = bdrv_file_open(&bs, filename, BDRV_O_RDONLY);
>> +    ret = bdrv_file_open(&bs, filename, 0);
>>      if (ret < 0)
>>          return NULL;
>>      ret = bdrv_pread(bs, 0, buf, sizeof(buf));
>> @@ -356,7 +356,7 @@ int bdrv_open(BlockDriverState *bs, const char 
>> *filename, int flags)
>>  int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
>>                 BlockDriver *drv)
>>  {
>> -    int ret, open_flags, try_rw;
>> +    int ret, open_flags;
>>      char tmp_filename[PATH_MAX];
>>      char backing_filename[PATH_MAX];
>>  
>> @@ -446,19 +446,23 @@ int bdrv_open2(BlockDriverState *bs, const char 
>> *filename, int flags,
>>  
>>      /* Note: for compatibility, we open disk image files as RDWR, and
>>         RDONLY as fallback */
>> -    try_rw = !bs->read_only || bs->is_temporary;
>> -    if (!(flags & BDRV_O_FILE))
>> -        open_flags = (try_rw ? BDRV_O_RDWR : 0) |
>> -            (flags & (BDRV_O_CACHE_MASK|BDRV_O_NATIVE_AIO));
>> -    else
>> +    bs->read_only = (flags & BDRV_O_RDWR) == 0;
> 
> !(flags & BDRV_O_RDWR) is a standard idiom, and it's more readable IMO.
> 
>> +    if (!(flags & BDRV_O_FILE)) {
>> +        open_flags = (flags & (BDRV_O_RDWR | 
>> BDRV_O_CACHE_MASK|BDRV_O_NATIVE_AIO));
>> +        if (bs->is_temporary) { /* snapshot should be writeable */
>> +            open_flags |= BDRV_O_RDWR;
>> +        }
>> +    } else {
>>          open_flags = flags & ~(BDRV_O_FILE | BDRV_O_SNAPSHOT);
>> -    if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv))
>> +    }
>> +    if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv)) {
>>          ret = -ENOTSUP;
>> -    else
>> +    } else {
>>          ret = drv->bdrv_open(bs, filename, open_flags);
>> -    if ((ret == -EACCES || ret == -EPERM) && !(flags & BDRV_O_FILE)) {
>> -        ret = drv->bdrv_open(bs, filename, open_flags & ~BDRV_O_RDWR);
>> -        bs->read_only = 1;
>> +        if ((ret == -EACCES || ret == -EPERM) && !(flags & BDRV_O_FILE)) {
>> +            ret = drv->bdrv_open(bs, filename, open_flags & ~BDRV_O_RDWR);
>> +            bs->read_only = 1;
>> +        }
>>      }
>>      if (ret < 0) {
>>          qemu_free(bs->opaque);
>> @@ -481,14 +485,13 @@ int bdrv_open2(BlockDriverState *bs, const char 
>> *filename, int flags,
>>          /* if there is a backing file, use it */
>>          BlockDriver *back_drv = NULL;
>>          bs->backing_hd = bdrv_new("");
>> -        /* pass on read_only property to the backing_hd */
>> -        bs->backing_hd->read_only = bs->read_only;
>>          path_combine(backing_filename, sizeof(backing_filename),
>>                       filename, bs->backing_file);
>>          if (bs->backing_format[0] != '\0')
>>              back_drv = bdrv_find_format(bs->backing_format);
>>          ret = bdrv_open2(bs->backing_hd, backing_filename, open_flags,
>>                           back_drv);
>> +        bs->backing_hd->read_only =  (open_flags & BDRV_O_RDWR) == 0;
> 
> !(open_flags & BDRV_O_RDWR) is a standard idiom and it's more readable
> IMO.

Sorry, I prefer the more verbose style. The extra bytes on me. Seems more 
readable for me.

> Further, pls don't put two spaces after ==.

Sure, will correct.

> 
>>          if (ret < 0) {
>>              bdrv_close(bs);
>>              return ret;
>> diff --git a/block.h b/block.h
>> index bee9ec5..fd4e8dd 100644
>> --- a/block.h
>> +++ b/block.h
>> @@ -27,9 +27,7 @@ typedef struct QEMUSnapshotInfo {
>>      uint64_t vm_clock_nsec; /* VM clock relative to boot */
>>  } QEMUSnapshotInfo;
>>  
>> -#define BDRV_O_RDONLY      0x0000
>>  #define BDRV_O_RDWR        0x0002
>> -#define BDRV_O_ACCESS      0x0003
>>  #define BDRV_O_CREAT       0x0004 /* create an empty file */
>>  #define BDRV_O_SNAPSHOT    0x0008 /* open the file read only and save 
>> writes in a snapshot */
>>  #define BDRV_O_FILE        0x0010 /* open as a raw file (do not try to
>> diff --git a/block/raw-posix.c b/block/raw-posix.c
>> index 5a6a22b..b427211 100644
>> --- a/block/raw-posix.c
>> +++ b/block/raw-posix.c
>> @@ -138,7 +138,7 @@ static int raw_open_common(BlockDriverState *bs, const 
>> char *filename,
>>  
>>      s->open_flags = open_flags | O_BINARY;
>>      s->open_flags &= ~O_ACCMODE;
>> -    if ((bdrv_flags & BDRV_O_ACCESS) == BDRV_O_RDWR) {
>> +    if (bdrv_flags & BDRV_O_RDWR) {
>>          s->open_flags |= O_RDWR;
>>      } else {
>>          s->open_flags |= O_RDONLY;
>> diff --git a/block/raw-win32.c b/block/raw-win32.c
>> index 72acad5..01a6d25 100644
>> --- a/block/raw-win32.c
>> +++ b/block/raw-win32.c
>> @@ -81,7 +81,7 @@ static int raw_open(BlockDriverState *bs, const char 
>> *filename, int flags)
>>  
>>      s->type = FTYPE_FILE;
>>  
>> -    if ((flags & BDRV_O_ACCESS) == O_RDWR) {
>> +    if (flags & BDRV_O_RDWR) {
>>          access_flags = GENERIC_READ | GENERIC_WRITE;
>>      } else {
>>          access_flags = GENERIC_READ;
>> @@ -337,7 +337,7 @@ static int hdev_open(BlockDriverState *bs, const char 
>> *filename, int flags)
>>      }
>>      s->type = find_device_type(bs, filename);
>>  
>> -    if ((flags & BDRV_O_ACCESS) == O_RDWR) {
>> +    if (flags & BDRV_O_RDWR) {
>>          access_flags = GENERIC_READ | GENERIC_WRITE;
>>      } else {
>>          access_flags = GENERIC_READ;
> 
> The above changes seem nothing to do with passing in parameter to the
> function. If the are intentional, pls mention them in changelog or split
> to a separate patch.

Correct, see my preface.

> 
>> diff --git a/block/vmdk.c b/block/vmdk.c
>> index 4e48622..ddc2fcb 100644
>> --- a/block/vmdk.c
>> +++ b/block/vmdk.c
>> @@ -357,7 +357,7 @@ static int vmdk_parent_open(BlockDriverState *bs, const 
>> char * filename)
>>              return -1;
>>          }
>>          parent_open = 1;
>> -        if (bdrv_open(bs->backing_hd, parent_img_name, BDRV_O_RDONLY) < 0)
>> +        if (bdrv_open(bs->backing_hd, parent_img_name, 0) < 0)
>>              goto failure;
>>          parent_open = 0;
>>      }
>> @@ -371,9 +371,10 @@ static int vmdk_open(BlockDriverState *bs, const char 
>> *filename, int flags)
>>      uint32_t magic;
>>      int l1_size, i, ret;
>>  
>> -    if (parent_open)
>> -        // Parent must be opened as RO.
>> -        flags = BDRV_O_RDONLY;
>> +    if (parent_open) {
>> +        /* Parent must be opened as RO, no RDWR. */
>> +        flags = 0;
>> +    }
>>  
>>      ret = bdrv_file_open(&s->hd, filename, flags);
>>      if (ret < 0)
>> diff --git a/hw/xen_disk.c b/hw/xen_disk.c
>> index 5c55251..beadf90 100644
>> --- a/hw/xen_disk.c
>> +++ b/hw/xen_disk.c
>> @@ -613,7 +613,7 @@ static int blk_init(struct XenDevice *xendev)
>>      qflags = BDRV_O_RDWR;
>>      } else {
>>      mode   = O_RDONLY;
>> -    qflags = BDRV_O_RDONLY;
>> +    qflags = 0;
>>      info  |= VDISK_READONLY;
>>      }
>>  
>> diff --git a/monitor.c b/monitor.c
>> index b824e7c..5bb8872 100644
>> --- a/monitor.c
>> +++ b/monitor.c
>> @@ -916,7 +916,7 @@ static void do_change_block(Monitor *mon, const char 
>> *device,
>>      }
>>      if (eject_device(mon, bs, 0) < 0)
>>          return;
>> -    bdrv_open2(bs, filename, 0, drv);
>> +    bdrv_open2(bs, filename, BDRV_O_RDWR, drv);
> 
> This and below seems to change file from rdwr to readonly.
> Intentional?

Yes, intentioanl. The default used to be read-write, even when passed nothing,
see old code citation from bdrv_open2:
======BEGIN======
    /* Note: for compatibility, we open disk image files as RDWR, and
       RDONLY as fallback */
    if (!(flags & BDRV_O_FILE))
        open_flags = BDRV_O_RDWR | (flags & BDRV_O_CACHE_MASK);
======END======
Now you need to explicitly ask what you want.

> 
>>      monitor_read_bdrv_key_start(mon, bs, NULL, NULL);
>>  }
>>  
>> diff --git a/qemu-img.c b/qemu-img.c
>> index 48b9315..3cea8ce 100644
>> --- a/qemu-img.c
>> +++ b/qemu-img.c
>> @@ -204,7 +204,7 @@ static BlockDriverState *bdrv_new_open(const char 
>> *filename,
>>      } else {
>>          drv = NULL;
>>      }
>> -    if (bdrv_open2(bs, filename, BRDV_O_FLAGS, drv) < 0) {
>> +    if (bdrv_open2(bs, filename, BRDV_O_FLAGS | BDRV_O_RDWR, drv) < 0) {
>>          error("Could not open '%s'", filename);
>>      }
>>      if (bdrv_is_encrypted(bs)) {
>> @@ -468,7 +468,7 @@ static int img_commit(int argc, char **argv)
>>      } else {
>>          drv = NULL;
>>      }
>> -    if (bdrv_open2(bs, filename, BRDV_O_FLAGS, drv) < 0) {
>> +    if (bdrv_open2(bs, filename, BRDV_O_FLAGS | BDRV_O_RDWR, drv) < 0) {
>>          error("Could not open '%s'", filename);
>>      }
>>      ret = bdrv_commit(bs);
>> @@ -966,10 +966,11 @@ static int img_snapshot(int argc, char **argv)
>>      BlockDriverState *bs;
>>      QEMUSnapshotInfo sn;
>>      char *filename, *snapshot_name = NULL;
>> -    int c, ret;
>> +    int c, ret, bdrv_oflags;
>>      int action = 0;
>>      qemu_timeval tv;
>>  
>> +    bdrv_oflags = BDRV_O_RDWR;
>>      /* Parse commandline parameters */
>>      for(;;) {
>>          c = getopt(argc, argv, "la:c:d:h");
>> @@ -985,6 +986,7 @@ static int img_snapshot(int argc, char **argv)
>>                  return 0;
>>              }
>>              action = SNAPSHOT_LIST;
>> +            bdrv_oflags &= ~BDRV_O_RDWR; /* no need for RW */
> 
> bdrv_oflags = BDRV_O_RDONLY would be clearer, and no need
> for comment then?

I had some thoughts about that. I added just few lines above the assignment:
'bdrv_oflags = BDRV_O_RDWR;'
so I could just overwrite it with:
'bdrv_oflags = 0; ' /* no  BDRV_O_RDONLY anymore */
but thought that's clearer.

> 
>>              break;
>>          case 'a':
>>              if (action) {
>> @@ -1022,7 +1024,7 @@ static int img_snapshot(int argc, char **argv)
>>      if (!bs)
>>          error("Not enough memory");
>>  
>> -    if (bdrv_open2(bs, filename, 0, NULL) < 0) {
>> +    if (bdrv_open2(bs, filename, bdrv_oflags, NULL) < 0) {
>>          error("Could not open '%s'", filename);
>>      }
>>  
>> diff --git a/qemu-io.c b/qemu-io.c
>> index 1c19b92..b159bc9 100644
>> --- a/qemu-io.c
>> +++ b/qemu-io.c
>> @@ -1359,10 +1359,9 @@ open_f(int argc, char **argv)
>>              }
>>      }
>>  
>> -    if (readonly)
>> -            flags |= BDRV_O_RDONLY;
>> -    else
>> -            flags |= BDRV_O_RDWR;
>> +    if (!readonly) {
>> +            flags |= BDRV_O_RDWR;
>> +        }
>>  
>>      if (optind != argc - 1)
>>              return command_usage(&open_cmd);
>> @@ -1506,10 +1505,9 @@ int main(int argc, char **argv)
>>      add_check_command(init_check_command);
>>  
>>      /* open the device */
>> -    if (readonly)
>> -            flags |= BDRV_O_RDONLY;
>> -    else
>> -            flags |= BDRV_O_RDWR;
>> +    if (!readonly) {
>> +            flags |= BDRV_O_RDWR;
>> +        }
> 
> alignment seems broken in 2 places above

Sure, will fix (both).

> 
>>  
>>      if ((argc - optind) == 1)
>>              openfile(argv[optind], flags, growable);
>> diff --git a/qemu-nbd.c b/qemu-nbd.c
>> index 6707ea5..4463679 100644
>> --- a/qemu-nbd.c
>> +++ b/qemu-nbd.c
>> @@ -213,7 +213,7 @@ int main(int argc, char **argv)
>>      int opt_ind = 0;
>>      int li;
>>      char *end;
>> -    int flags = 0;
>> +    int flags = BDRV_O_RDWR;
>>      int partition = -1;
>>      int ret;
>>      int shared = 1;
>> diff --git a/vl.c b/vl.c
>> index 76ef8ca..eee59dd 100644
>> --- a/vl.c
>> +++ b/vl.c
>> @@ -2227,19 +2227,19 @@ DriveInfo *drive_init(QemuOpts *opts, void *opaque,
>>      }
>>  
>>      if (ro == 1) {
>> -        if (type == IF_IDE) {
>> -            fprintf(stderr, "qemu: readonly flag not supported for drive 
>> with ide interface\n");
>> +        if (type != IF_SCSI && type != IF_VIRTIO && type != IF_FLOPPY) {
> 
> So each new user will have to be added here? Any idea how todo this
> better? Can't relevant drive emulation check read_only flag and report
> an error? Or set a flag in drive info declaring readonly support.

Right. Second options seems better to me. Will do.

> 
>> +            fprintf(stderr, "qemu: readonly flag not supported for drive 
>> with this interface\n");
>>              return NULL;
>>          }
>> -        (void)bdrv_set_read_only(dinfo->bdrv, 1);
>>      }
>>      /* 
>>       * cdrom is read-only. Set it now, after above interface checking
>>       * since readonly attribute not explicitly required, so no error.
>>       */
>>      if (media == MEDIA_CDROM) {
>> -        (void)bdrv_set_read_only(dinfo->bdrv, 1);
>> +        ro = 1;
>>      }
>> +    bdrv_flags |= ro ? 0 : BDRV_O_RDWR;
>>  
>>      if (bdrv_open2(dinfo->bdrv, file, bdrv_flags, drv) < 0) {
>>          fprintf(stderr, "qemu: could not open disk image %s: %s\n",
>> -- 
>> 1.6.3.3
>>
>>

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