[Qemu-devel] [Bug 1776920] Re: qemu-img convert on Mac OSX creates corrupt images

[Yan-Jie Wang]

I have done some experiments and find out that 
the behavior of lseek with whence set to SEEK_DATA is different from the 
behavior of Linux's lseek.

If the supplied offset is in the middle of a data region, it returns the
start of the next data region.  There may be many data regions in a big
file even though it has no hole.

return value of lseek with whence set to SEEK_DATA:

|--(offset)--Data----|(return value)----Data----|
|--(offset)--Data----|----Hole----|(return value)----Data----|


** Patch added: "macOS-lseek.patch"
   
https://bugs.launchpad.net/qemu/+bug/1776920/+attachment/5186138/+files/macOS-lseek.patch

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https://bugs.launchpad.net/bugs/1776920

Title:
  qemu-img convert on Mac OSX creates corrupt images

Status in QEMU:
  New

Bug description:
  An image created by qemu-img create, then modified by another program
  is converted to bad/corrupt image when using convert sub command on
  Mac OSX. The same convert works on Linux. The version of qemu-img is
  2.12.

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