blockjob: refactor backup_start as backup_job_create

Refactor backup_start as backup_job_create, which only creates the job,
but does not automatically start it. The old interface, 'backup_start',
is not kept in favor of limiting the number of nearly-identical interfaces
that would have to be edited to keep up with QAPI changes in the future.

Callers that wish to synchronously start the backup_block_job can
instead just call block_job_start immediately after calling
backup_job_create.

Transactions are updated to use the new interface, calling block_job_start
only during the .commit phase, which helps prevent race conditions where
jobs may finish before we even finish building the transaction. This may
happen, for instance, during empty block backup jobs.

Reported-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 1478587839-9834-6-git-send-email-jsnow@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>
4 files changed
tree: 60b90cb15047f7da10623da590f61c2500895cdc
  1. audio/
  2. backends/
  3. block/
  4. bsd-user/
  5. contrib/
  6. crypto/
  7. default-configs/
  8. disas/
  9. docs/
  10. fpu/
  11. fsdev/
  12. gdb-xml/
  13. hw/
  14. include/
  15. io/
  16. libdecnumber/
  17. linux-headers/
  18. linux-user/
  19. migration/
  20. nbd/
  21. net/
  22. pc-bios/
  23. po/
  24. qapi/
  25. qga/
  26. qobject/
  27. qom/
  28. replay/
  29. roms/
  30. scripts/
  31. slirp/
  32. stubs/
  33. target-alpha/
  34. target-arm/
  35. target-cris/
  36. target-i386/
  37. target-lm32/
  38. target-m68k/
  39. target-microblaze/
  40. target-mips/
  41. target-moxie/
  42. target-openrisc/
  43. target-ppc/
  44. target-s390x/
  45. target-sh4/
  46. target-sparc/
  47. target-tilegx/
  48. target-tricore/
  49. target-unicore32/
  50. target-xtensa/
  51. tcg/
  52. tests/
  53. trace/
  54. ui/
  55. util/
  56. .dir-locals.el
  57. .exrc
  58. .gitignore
  59. .gitmodules
  60. .mailmap
  61. .travis.yml
  62. accel.c
  63. aio-posix.c
  64. aio-win32.c
  65. arch_init.c
  66. async.c
  67. atomic_template.h
  68. balloon.c
  69. block.c
  70. blockdev-nbd.c
  71. blockdev.c
  72. blockjob.c
  73. bootdevice.c
  74. bt-host.c
  75. bt-vhci.c
  76. Changelog
  77. CODING_STYLE
  78. configure
  79. COPYING
  80. COPYING.LIB
  81. cpu-exec-common.c
  82. cpu-exec.c
  83. cpus-common.c
  84. cpus.c
  85. cputlb.c
  86. device-hotplug.c
  87. device_tree.c
  88. disas.c
  89. dma-helpers.c
  90. dump.c
  91. exec.c
  92. gdbstub.c
  93. HACKING
  94. hmp-commands-info.hx
  95. hmp-commands.hx
  96. hmp.c
  97. hmp.h
  98. iohandler.c
  99. ioport.c
  100. iothread.c
  101. kvm-all.c
  102. kvm-stub.c
  103. LICENSE
  104. main-loop.c
  105. MAINTAINERS
  106. Makefile
  107. Makefile.objs
  108. Makefile.target
  109. memory.c
  110. memory_mapping.c
  111. module-common.c
  112. monitor.c
  113. numa.c
  114. os-posix.c
  115. os-win32.c
  116. page_cache.c
  117. qapi-schema.json
  118. qdev-monitor.c
  119. qdict-test-data.txt
  120. qemu-bridge-helper.c
  121. qemu-char.c
  122. qemu-doc.texi
  123. qemu-ga.texi
  124. qemu-img-cmds.hx
  125. qemu-img.c
  126. qemu-img.texi
  127. qemu-io-cmds.c
  128. qemu-io.c
  129. qemu-nbd.c
  130. qemu-nbd.texi
  131. qemu-option-trace.texi
  132. qemu-options-wrapper.h
  133. qemu-options.h
  134. qemu-options.hx
  135. qemu-seccomp.c
  136. qemu-tech.texi
  137. qemu-timer.c
  138. qemu.nsi
  139. qemu.sasl
  140. qmp.c
  141. qtest.c
  142. README
  143. replication.c
  144. replication.h
  145. rules.mak
  146. softmmu_template.h
  147. spice-qemu-char.c
  148. tcg-runtime.c
  149. tci.c
  150. thread-pool.c
  151. thunk.c
  152. tpm.c
  153. trace-events
  154. translate-all.c
  155. translate-all.h
  156. translate-common.c
  157. user-exec.c
  158. VERSION
  159. version.rc
  160. vl.c
  161. xen-common-stub.c
  162. xen-common.c
  163. xen-hvm-stub.c
  164. xen-hvm.c
  165. xen-mapcache.c