The readdir_r() function has a broken design and should not be used anymore. It is expected to be obsoleted in a future version of POSIX.1:
http://austingroupbugs.net/view.php?id=696#c2857 Glibc has already announced that 2.24 (scheduled for August 2016) will deprecates readdir_r() and encourages people to use readdir() with external synchronization instead. This series replaces readdir_r() by readdir() and changes the internal API in fsdev/file-op-9p.h to be readdir-like, like it was before commit "5f524c1ebcc5 use readdir_r instead of readdir for reentrancy". The 9p code runs in coroutines, called either: - from the QEMU main-loop when ioventfd=on, which is the default, or - from vCPU context when ioeventfd=off, with the qemu_global_mutex taken All hypothetical critical sections around the use of readdir() are then already serialized. This series introduces a serialization anyway for the code to be fully independant from the context. Since POSIX.1 will require readdir() to be thread-safe when employed on different directory streams, and glibc already does that, the choice was made to have per-directory locking. This is acceptable because VirtFS support is disabled in configure for non-linux hosts. Unsurprisingly, there is no contention and the locking/unlocking hasn't any noticeable impact on performance. Since early glibc-2.24 users are already encountering build breaks, I guess this should go upstream sooner than later. I plan to issue a pull request next week, or even before if possible. Please comment ! Thanks. --- Greg Kurz (4): 9p: drop useless out: label 9p: introduce the V9fsDir type 9p: add locking to V9fsDir 9p: switch back to readdir() fsdev/file-op-9p.h | 3 +- hw/9pfs/9p-handle.c | 24 +++++++++----------- hw/9pfs/9p-local.c | 36 ++++++++++++++++-------------- hw/9pfs/9p-proxy.c | 26 ++++++++++----------- hw/9pfs/9p-synth.c | 23 ++++++++----------- hw/9pfs/9p-synth.h | 1 + hw/9pfs/9p.c | 62 ++++++++++++++++++++++++++++++--------------------- hw/9pfs/9p.h | 22 +++++++++++++++++- hw/9pfs/codir.c | 10 +++++--- hw/9pfs/coth.h | 3 +- 10 files changed, 119 insertions(+), 91 deletions(-) -- Greg
