In macOS, lseek with SEEK_DATA behaves differently.
It seeks to the next data region even though offset is in the middle of
a data region. In addition, there may be many data regions without any
hole among them, like this: |---Data---|---Data---|
Because of this, qemu-img convert with raw images as input may create
corrupted images in macOS especially for large files, and qemu-img
map may also report wrong things. This patch fixes this undesired
behaviors.
Signed-off-by: Yan-Jie Wang <jaywang0...@gmail.com>
---
block/file-posix.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 59 insertions(+)
diff --git a/block/file-posix.c b/block/file-posix.c
index fe83cbf0eb..5c208580e6 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -2325,6 +2325,7 @@ static int find_allocation(BlockDriverState *bs, off_t
start,
BDRVRawState *s = bs->opaque;
off_t offs;
+#if !(defined(__APPLE__) && defined(__MACH__))
/*
* SEEK_DATA cases:
* D1. offs == start: start is in data
@@ -2395,6 +2396,64 @@ static int find_allocation(BlockDriverState *bs, off_t
start,
*hole = offs;
return 0;
}
+#else
+ /*
+ * In macOS, lseek with SEEK_DATA seeks to the next data region
+ * even though the offset is in the middle of a data region.
+ * In addition, there may be many data regions without any holes among
+ * them, like this: |----Data----|----Data----|
+ *
+ * Although the behavior of lseek with SEEK_DATA is different in macOS,
+ * the behavior of lseek with SEEK_HOLE in macOS is the same as the one in
+ * Linux.
+ *
+ * Therefore, the cases D1, D2 and H2 are changed to the followings
+ * for macOS:
+ * D1. offs == start: start is at the beginning of a data region.
+ * D2. offs > start: either start is in a hole, next data at offs
+ * or start is in the middle of a data region,
+ * next data at offs.
+ * H2. offs > start: start is in data, next hole at offs
+ */
+
+ offs = lseek(s->fd, start, SEEK_HOLE);
+ if (offs < 0) {
+ return -errno; /* H3 or H4 */
+ }
+
+ if (offs < start) {
+ /* This is not a valid return by lseek(). We are safe to just return
+ * -EIO in this case, and we'll treat it like D4. */
+ return -EIO;
+ }
+
+ if (offs > start) {
+ /* H2: start is in data, next hole at offs */
+ *data = start;
+ *hole = offs;
+ return 0;
+ }
+
+ /* H1: start is in a hole */
+ offs = lseek(s->fd, start, SEEK_DATA);
+
+ if (offs < 0) {
+ return -errno; /* H1 and (D3 or D4) */
+ }
+
+ if (offs < start) {
+ /* This is not a valid return by lseek(). We are safe to just return
+ * -EIO in this case, and we'll treat it like D4. */
+ return -EIO;
+ }
+
+ if (offs > start) {
+ /* H1 and D2: start is in a hole, next data at offs */
+ *hole = start;
+ *data = offs;
+ return 0;
+ }
+#endif
/* D1 and H1 */
return -EBUSY;
--
2.18.0
