Re: [Qemu-devel] [PATCH v2 2/5] block: Use error code EMEDIUMTYPE for wrong format in some block drivers

[Markus Armbruster]

Stefan Weil <address@hidden> writes:

> Am 18.01.2013 09:53, schrieb Markus Armbruster:
>> Stefan Weil <address@hidden> writes:
>>> This improves error reports for bochs, cow, qcow, qcow2, qed and vmdk
>>> when a file with the wrong format is selected.
>>>
>>> Signed-off-by: Stefan Weil <address@hidden>
>>> ---
>>>  block/bochs.c |    2 +-
>>>  block/cow.c   |    2 +-
>>>  block/qcow.c  |    2 +-
>>>  block/qcow2.c |    2 +-
>>>  block/qed.c   |    2 +-
>>>  block/vmdk.c  |    4 ++--
>>>  6 files changed, 7 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/block/bochs.c b/block/bochs.c
>>> index 1b1d9cd..3737583 100644
>>> --- a/block/bochs.c
>>> +++ b/block/bochs.c
>>> @@ -126,7 +126,7 @@ static int bochs_open(BlockDriverState *bs, int flags)
>>>          strcmp(bochs.subtype, GROWING_TYPE) ||
>>>     ((le32_to_cpu(bochs.version) != HEADER_VERSION) &&
>>>     (le32_to_cpu(bochs.version) != HEADER_V1))) {
>>> -        goto fail;
>>> +        return -EMEDIUMTYPE;
>>>      }
>>>  
>>>      if (le32_to_cpu(bochs.version) == HEADER_V1) {
>> You make the function return either 0, -1 or -EMEDIUMTYPE.  Please make
>> it return either 0 or a negative errno code, like this (untested):
>
> Hi Markus,
>
> returning 0, -1 is like before, only returning -EMEDIUMTYPE is new.
>
> You are right, a return value of -1 should be replaced by a negative
> error value. I fixed this for block/vdi.c in a separate patch as
> suggested by Kevin, see http://patchwork.ozlabs.org/patch/213375/.
>
> The same kind of improvement should be done for other block
> drivers which currently use -1, but that can be done after my
> patch series was applied.
>
> The primary purpose of my patch series was fixing open bugreports.
> For vdi I did more because I feel responsible for that part of the
> code.

I had a closer look at the various bdrv_open() methods, and how they're
used.  Turns out that we already assume they return 0/-errno, yet the
following methods return -1 on some or all errors:

    bochs_open 
    cloop_open
    dmg_open
    parallels_open
    vdi_open
    vpc_open

They all need to be fixed.  I appreciate you fixing vdi_open().

However, you "improve" bochs_open() from completely and obviously broken
(return -1 on error always) to half-broken (return -1 on some errors,
and -errno on others).  I don't like that.

Fixing it up doesn't look hard to me (sketch appended).  Could you do
that for us?

If not, I'd prefer to leave bochs_open() completely and obviously
broken.




diff --git a/block/bochs.c b/block/bochs.c
index 1b1d9cd..57b2dc8 100644
--- a/block/bochs.c
+++ b/block/bochs.c
@@ -111,13 +111,14 @@ static int bochs_probe(const uint8_t *buf, int buf_size, 
const char *filename)
 static int bochs_open(BlockDriverState *bs, int flags)
 {
     BDRVBochsState *s = bs->opaque;
-    int i;
+    int ret, i;
     struct bochs_header bochs;
     struct bochs_header_v1 header_v1;
 
     bs->read_only = 1; // no write support yet
 
-    if (bdrv_pread(bs->file, 0, &bochs, sizeof(bochs)) != sizeof(bochs)) {
+    ret = bdrv_pread(bs->file, 0, &bochs, sizeof(bochs));
+    if (ret < 0) {
         goto fail;
     }
 
@@ -126,6 +127,7 @@ static int bochs_open(BlockDriverState *bs, int flags)
         strcmp(bochs.subtype, GROWING_TYPE) ||
        ((le32_to_cpu(bochs.version) != HEADER_VERSION) &&
        (le32_to_cpu(bochs.version) != HEADER_V1))) {
+        ret = -EMEDIUMTYPE;
         goto fail;
     }
 
@@ -138,8 +140,9 @@ static int bochs_open(BlockDriverState *bs, int flags)
 
     s->catalog_size = le32_to_cpu(bochs.extra.redolog.catalog);
     s->catalog_bitmap = g_malloc(s->catalog_size * 4);
-    if (bdrv_pread(bs->file, le32_to_cpu(bochs.header), s->catalog_bitmap,
-                   s->catalog_size * 4) != s->catalog_size * 4)
+    ret = bdrv_pread(bs->file, le32_to_cpu(bochs.header), s->catalog_bitmap,
+                     s->catalog_size * 4);
+    if (ret < 0)
        goto fail;
     for (i = 0; i < s->catalog_size; i++)
        le32_to_cpus(&s->catalog_bitmap[i]);
@@ -154,7 +157,7 @@ static int bochs_open(BlockDriverState *bs, int flags)
     qemu_co_mutex_init(&s->lock);
     return 0;
  fail:
-    return -1;
+    return ret;
 }
 
 static int64_t seek_to_sector(BlockDriverState *bs, int64_t sector_num)