See comment in code and https://www.redhat.com/archives/libguestfs/2020-August/msg00023.html --- plugins/vddk/vddk.c | 32 ++++++++++++++++++++++++++++---- 1 file changed, 28 insertions(+), 4 deletions(-) diff --git a/plugins/vddk/vddk.c b/plugins/vddk/vddk.c index 31e58f66..95e030d4 100644 --- a/plugins/vddk/vddk.c +++ b/plugins/vddk/vddk.c @@ -511,17 +511,29 @@ vddk_dump_plugin (void) #endif } -/* XXX To really do threading correctly in accordance with the VDDK - * documentation, we must do all open/close calls from a single - * thread. This is a huge pain. +/* The rules on threads and VDDK are here: + * https://code.vmware.com/docs/11750/virtual-disk-development-kit-programmi... + * + * Before nbdkit 1.22 we used SERIALIZE_ALL_REQUESTS. Since nbdkit + * 1.22 we changed this to SERIALIZE_REQUESTS and added a mutex around + * calls to VixDiskLib_Open and VixDiskLib_Close. This is not quite + * within the letter of the rules, but is within the spirit. + * + * We also enabled multi-conn for readonly connections since it + * appears possible for clients to open multiple handles even if they + * point to the same server/disk. */ -#define THREAD_MODEL NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS +#define THREAD_MODEL NBDKIT_THREAD_MODEL_SERIALIZE_REQUESTS + +/* Lock protecting open/close calls - see above. */ +static pthread_mutex_t open_close_lock = PTHREAD_MUTEX_INITIALIZER; /* The per-connection handle. */ struct vddk_handle { VixDiskLibConnectParams *params; /* connection parameters */ VixDiskLibConnection connection; /* connection */ VixDiskLibHandle handle; /* disk handle */ + int readonly; }; static inline VixDiskLibConnectParams * @@ -557,6 +569,7 @@ free_connect_params (VixDiskLibConnectParams *params) static void * vddk_open (int readonly) { + ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&open_close_lock); struct vddk_handle *h; VixError err; uint32_t flags; @@ -567,6 +580,7 @@ vddk_open (int readonly) return NULL; } + h->readonly = readonly; h->params = allocate_connect_params (); if (h->params == NULL) { nbdkit_error ("allocate VixDiskLibConnectParams: %m"); @@ -649,6 +663,7 @@ vddk_open (int readonly) static void vddk_close (void *handle) { + ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&open_close_lock); struct vddk_handle *h = handle; DEBUG_CALL ("VixDiskLib_Close", "handle"); @@ -659,6 +674,14 @@ vddk_close (void *handle) free (h); } +/* Allow multi-conn - see comment about threading above. */ +static int +vddk_can_multi_conn (void *handle) +{ + struct vddk_handle *h = handle; + return h->readonly; +} + /* Get the file size. */ static int64_t vddk_get_size (void *handle) @@ -986,6 +1009,7 @@ static struct nbdkit_plugin plugin = { .after_fork = vddk_after_fork, .open = vddk_open, .close = vddk_close, + .can_multi_conn = vddk_can_multi_conn, .get_size = vddk_get_size, .pread = vddk_pread, .pwrite = vddk_pwrite, -- 2.27.0