A domid is considered retired if the domain it represents was destroyed less than a specified number of seconds ago. The number can be set using the environment variable LIBXL_DOMID_MAX_RETIREMENT. If the variable does not exist then a default value of 60s is used.
Whenever a domain is destroyed, a time-stamped record will be written into a history file (/var/run/xen/domid-history). To avoid the history file growing too large, any records with time-stamps that indicate that the domid has exceeded maximum retirement will also be purged. A new utility function, libxl__is_retired_domid(), has been added. This function reads the same history file checking whether a specified domid has a record that does not exceed maximum retirement. Since this utility function does not write to the file, no records are actually purged by it. NOTE: Since the history file is hosted by a tmpfs file system, it is automatically purged on boot thus allowing safe use of CLOCK_MONOTONIC as a time source. Signed-off-by: Paul Durrant <pdurr...@amazon.com> --- Cc: Ian Jackson <ian.jack...@eu.citrix.com> Cc: Wei Liu <w...@xen.org> Cc: Anthony PERARD <anthony.per...@citrix.com> v2: - New in v2 --- tools/libxl/libxl_domain.c | 132 +++++++++++++++++++++++++++++++++++ tools/libxl/libxl_internal.h | 10 +++ 2 files changed, 142 insertions(+) diff --git a/tools/libxl/libxl_domain.c b/tools/libxl/libxl_domain.c index 5714501778..7f255f184c 100644 --- a/tools/libxl/libxl_domain.c +++ b/tools/libxl/libxl_domain.c @@ -1268,6 +1268,137 @@ static void dm_destroy_cb(libxl__egc *egc, libxl__devices_destroy(egc, &dis->drs); } +static unsigned int libxl__get_max_retirement(void) +{ + const char *env_max_retirement = getenv("LIBXL_DOMID_MAX_RETIREMENT"); + + return env_max_retirement ? strtol(env_max_retirement, NULL, 0) : + LIBXL_DOMID_MAX_RETIREMENT; +} + +static int libxl__open_domid_history(libxl__gc *gc) +{ + const char *name; + int fd; + int ret; + + name = GCSPRINTF("%s/domid-history", libxl__run_dir_path()); + + fd = open(name, O_RDWR|O_CREAT, 0644); + if (fd < 0) { + LOGE(ERROR, "unexpected error while trying open %s, errno=%d", + name, errno); + goto fail; + } + + for (;;) { + ret = flock(fd, LOCK_EX); + if (!ret) + break; + if (errno != EINTR) { + /* All other errno: EBADF, EINVAL, ENOLCK, EWOULDBLOCK */ + LOGE(ERROR, + "unexpected error while trying to lock %s, fd=%d, errno=%d", + name, fd, errno); + goto fail; + } + } + + return fd; + +fail: + if (fd >= 0) + close(fd); + + return -1; +} + +/* Write a domid retirement record */ +static void libxl__retire_domid(libxl__gc *gc, uint32_t domid) +{ + long max_retirement = libxl__get_max_retirement(); + int fd; + FILE *f; + long roff, woff; + char line[64]; + struct timespec ts; + + fd = libxl__open_domid_history(gc); + if (fd < 0) + return; + + clock_gettime(CLOCK_MONOTONIC, &ts); + + /* Purge old retirement records */ + + f = fdopen(fd, "r+"); + woff = ftell(f); + + while (fgets(line, sizeof(line), f)) { + unsigned long sec; + unsigned int ignored; + + roff = ftell(f); + + if (sscanf(line, "%lu %u", &sec, &ignored) != 2) + continue; /* Purge malformed lines */ + + if (ts.tv_sec - sec > max_retirement) + continue; + + fseek(f, woff, SEEK_SET); + fputs(line, f); + woff = ftell(f); + + fseek(f, roff, SEEK_SET); + } + + fseek(f, woff, SEEK_SET); + fprintf(f, "%lu %u\n", ts.tv_sec, domid); + woff = ftell(f); + fflush(f); + + ftruncate(fd, woff); /* may now be fewer records */ + + close(fd); +} + +bool libxl__is_retired_domid(libxl__gc *gc, uint32_t domid) +{ + long max_retirement = libxl__get_max_retirement(); + bool retired = false; + int fd; + FILE *f; + char line[64]; + struct timespec ts; + + fd = libxl__open_domid_history(gc); + if (fd < 0) + return false; + + clock_gettime(CLOCK_MONOTONIC, &ts); + + f = fdopen(fd, "r"); + + while (fgets(line, sizeof(line), f)) { + unsigned long sec; + unsigned int check; + + if (sscanf(line, "%lu %u", &sec, &check) != 2) + continue; + + if (check == domid && + ts.tv_sec - sec <= max_retirement) { + retired = true; + break; + } + } + + close(fd); + + return retired; +} + static void devices_destroy_cb(libxl__egc *egc, libxl__devices_remove_state *drs, int rc) @@ -1331,6 +1462,7 @@ static void devices_destroy_cb(libxl__egc *egc, if (!ctx->xch) goto badchild; if (!dis->soft_reset) { + libxl__retire_domid(gc, domid); rc = xc_domain_destroy(ctx->xch, domid); } else { rc = xc_domain_pause(ctx->xch, domid); diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h index cb23490c59..fcac8a93c5 100644 --- a/tools/libxl/libxl_internal.h +++ b/tools/libxl/libxl_internal.h @@ -4770,6 +4770,16 @@ _hidden int libxl__domain_pvcontrol(libxl__egc *egc, libxl__xswait_state *pvcontrol, domid_t domid, const char *cmd); +/* + * Maximum number of seconds a domid remains in retirement after domain + * destruction. This can be overidden by the environment variable of the + * same name. + */ +#define LIBXL_DOMID_MAX_RETIREMENT 60 + +/* Check whether a domid is in retirement */ +bool libxl__is_retired_domid(libxl__gc *gc, uint32_t domid); + #endif /* -- 2.20.1 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel