Re: [PATCH v4 7/7] block: detect DKIOCGETBLOCKCOUNT/SIZE before use

[Max Reitz]

On 08.06.21 15:16, Paolo Bonzini wrote:
From: Joelle van Dyne <j...@getutm.app>
iOS hosts do not have these defined so we fallback to the
default behaviour.

Co-authored-by: Warner Losh <i...@bsdimp.com>
Reviewed-by: Peter Maydell <peter.mayd...@linaro.org>
Signed-off-by: Joelle van Dyne <j...@getutm.app>
Message-Id: <20210315180341.31638-...@getutm.app>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
  block/file-posix.c | 21 +++++++++------------
  1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 5821e1afed..4e2f7cf508 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -2322,8 +2322,11 @@ static int64_t raw_getlength(BlockDriverState *bs)
  again:
  #endif
      if (!fstat(fd, &sb) && (S_IFCHR & sb.st_mode)) {
+        size = 0;
  #ifdef DIOCGMEDIASIZE
-        if (ioctl(fd, DIOCGMEDIASIZE, (off_t *)&size))
+        if (ioctl(fd, DIOCGMEDIASIZE, (off_t *)&size)) {
+            size = 0;
+        }
  #elif defined(DIOCGPART)
          {
                  struct partinfo pi;
@@ -2332,9 +2335,7 @@ again:
                  else
                          size = 0;
          }
-        if (size == 0)
-#endif
-#if defined(__APPLE__) && defined(__MACH__)
+#elif defined(DKIOCGETBLOCKCOUNT) && defined(DKIOCGETBLOCKSIZE)

In v3, I was wondering whether it’s intentional that the following 
DKIOCGETBLOCKCOUNT/SIZE block would no longer be used as a fallback if 
the DIOCGMEDIASIZE ioctl failed (which it was before this patch).  I’m 
still wondering.

Max

          {
              uint64_t sectors = 0;
              uint32_t sector_size = 0;
@@ -2342,19 +2343,15 @@ again:
              if (ioctl(fd, DKIOCGETBLOCKCOUNT, &sectors) == 0
                 && ioctl(fd, DKIOCGETBLOCKSIZE, &sector_size) == 0) {
                  size = sectors * sector_size;
-            } else {
-                size = lseek(fd, 0LL, SEEK_END);
-                if (size < 0) {
-                    return -errno;
-                }
              }
          }
-#else
-        size = lseek(fd, 0LL, SEEK_END);
+#endif
+        if (size == 0) {
+            size = lseek(fd, 0LL, SEEK_END);
+        }
          if (size < 0) {
              return -errno;
          }
-#endif
  #if defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
          switch(s->type) {
          case FTYPE_CD: