A domid is considered recent if the domain it represents was destroyed less than a specified number of seconds ago. For debugging and/or testing purposes the number can be set using the environment variable LIBXL_DOMID_REUSE_TIMEOUT. 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 age of a domid has exceeded the re-use timeout will also be purged. A new utility function, libxl__is_recent_domid(), has been added. This function reads the same history file checking whether a specified domid has a record that does not exceed the re-use timeout. Since this utility function does not write to the file, no records are actually purged by it. NOTE: The history file is purged on boot to it is safe to use 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> v5: - Re-work file manipulation some more - Add more error checks v4: - Use new generalised libxl__flock - Don't read and write the same file - Use 'recent' rather than 'retired' - Add code into xen-init-dom0 to delete an old history file at boot v2: - New in v2 --- tools/helpers/xen-init-dom0.c | 30 +++++ tools/libxl/libxl.h | 2 + tools/libxl/libxl_domain.c | 204 ++++++++++++++++++++++++++++++++++ tools/libxl/libxl_internal.c | 10 ++ tools/libxl/libxl_internal.h | 14 +++ 5 files changed, 260 insertions(+) diff --git a/tools/helpers/xen-init-dom0.c b/tools/helpers/xen-init-dom0.c index a1e5729458..56f69ab66f 100644 --- a/tools/helpers/xen-init-dom0.c +++ b/tools/helpers/xen-init-dom0.c @@ -12,6 +12,32 @@ #define DOMNAME_PATH "/local/domain/0/name" #define DOMID_PATH "/local/domain/0/domid" +int clear_domid_history(void) +{ + int rc = 1; + xentoollog_logger_stdiostream *logger; + libxl_ctx *ctx; + + logger = xtl_createlogger_stdiostream(stderr, XTL_ERROR, 0); + if (!logger) + return 1; + + if (libxl_ctx_alloc(&ctx, LIBXL_VERSION, 0, + (xentoollog_logger *)logger)) { + fprintf(stderr, "cannot init libxl context\n"); + goto outlog; + } + + if (!libxl_clear_domid_history(ctx)) + rc = 0; + + libxl_ctx_free(ctx); + +outlog: + xtl_logger_destroy((xentoollog_logger *)logger); + return rc; +} + int main(int argc, char **argv) { int rc; @@ -70,6 +96,10 @@ int main(int argc, char **argv) if (rc) goto out; + rc = clear_domid_history(); + if (rc) + goto out; + /* Write xenstore entries. */ if (!xs_write(xsh, XBT_NULL, DOMID_PATH, "0", strlen("0"))) { fprintf(stderr, "cannot set domid for Dom0\n"); diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h index 18c1a2d6bf..1d235ecb1c 100644 --- a/tools/libxl/libxl.h +++ b/tools/libxl/libxl.h @@ -2657,6 +2657,8 @@ static inline int libxl_qemu_monitor_command_0x041200(libxl_ctx *ctx, #include <libxl_event.h> +int libxl_clear_domid_history(libxl_ctx *ctx); + #endif /* LIBXL_H */ /* diff --git a/tools/libxl/libxl_domain.c b/tools/libxl/libxl_domain.c index 973fc1434d..5349defcf0 100644 --- a/tools/libxl/libxl_domain.c +++ b/tools/libxl/libxl_domain.c @@ -1268,6 +1268,208 @@ static void dm_destroy_cb(libxl__egc *egc, libxl__devices_destroy(egc, &dis->drs); } +static unsigned int libxl__get_domid_reuse_timeout(void) +{ + const char *env_timeout = getenv("LIBXL_DOMID_REUSE_TIMEOUT"); + + return env_timeout ? strtol(env_timeout, NULL, 0) : + LIBXL_DOMID_REUSE_TIMEOUT; +} + +char *libxl__domid_history_path(libxl__gc *gc, const char *suffix) +{ + return GCSPRINTF("%s/domid-history%s", libxl__run_dir_path(), + suffix ?: ""); +} + +int libxl_clear_domid_history(libxl_ctx *ctx) +{ + GC_INIT(ctx); + char *path; + int rc = ERROR_FAIL; + + path = libxl__domid_history_path(gc, NULL); + if (!path) + goto out; + + if (unlink(path) < 0 && errno != ENOENT) { + LOGE(ERROR, "failed to remove '%s'\n", path); + goto out; + } + + rc = 0; + +out: + GC_FREE; + return rc; +} + +static bool libxl__read_recent(FILE *f, unsigned long *sec, + unsigned int *domid) +{ + int n; + + assert(f); + + n = fscanf(f, "%lu %u", sec, domid); + if (n == EOF) + return false; + else if (n != 2) /* malformed entry */ + *domid = INVALID_DOMID; + + return true; +} + +static bool libxl__write_recent(FILE *f, unsigned long sec, + unsigned int domid) +{ + assert(f); + assert(libxl_domid_valid_guest(domid)); + + return fprintf(f, "%lu %u\n", sec, domid) > 0; +} + +static int libxl__mark_domid_recent(libxl__gc *gc, uint32_t domid) +{ + long timeout = libxl__get_domid_reuse_timeout(); + libxl__flock *lock; + char *old, *new; + FILE *of = NULL, *nf = NULL; + struct timespec ts; + int rc = ERROR_FAIL; + + lock = libxl__lock_domid_history(gc); + if (!lock) { + LOGED(ERROR, domid, "failed to acquire lock"); + goto out; + } + + old = libxl__domid_history_path(gc, NULL); + of = fopen(old, "r"); + if (!of && errno != ENOENT) + LOGED(WARN, domid, "failed to open '%s'", old); + + new = libxl__domid_history_path(gc, ".new"); + nf = fopen(new, "a"); + if (!nf) { + LOGED(ERROR, domid, "failed to open '%s'", new); + goto out; + } + + if (clock_gettime(CLOCK_MONOTONIC, &ts)) { + LOGED(ERROR, domid, "failed to get time"); + goto out; + } + + if (of) { + unsigned long sec; + unsigned int val; + + while (libxl__read_recent(of, &sec, &val)) { + if (!libxl_domid_valid_guest(val)) + continue; /* Ignore invalid entries */ + + if (ts.tv_sec - sec > timeout) + continue; /* Ignore expired entries */ + + if (!libxl__write_recent(nf, sec, val)) { + LOGED(ERROR, domid, "failed to write to '%s'", new); + goto out; + } + } + if (ferror(of)) { + LOGED(ERROR, domid, "failed to read from '%s'", old); + goto out; + } + } + + if (!libxl__write_recent(nf, ts.tv_sec, domid)) { + LOGED(ERROR, domid, "failed to write to '%s'", new); + goto out; + } + + if (fclose(nf) == EOF) { + LOGED(ERROR, domid, "failed to close '%s'", new); + nf = NULL; + goto out; + } + nf = NULL; + + if (of && fclose(of) == EOF) { + LOGED(ERROR, domid, "failed to close '%s'", old); + of = NULL; + goto out; + } + of = NULL; + + if (rename(new, old) < 0) { + LOGED(ERROR, domid, "failed to rename '%s' -> '%s'", old, new); + goto out; + } + rc = 0; + +out: + if (nf) fclose(nf); + if (of) fclose(of); + if (lock) libxl__unlock_file(lock); + + return rc; +} + +int libxl__is_domid_recent(libxl__gc *gc, uint32_t domid, bool *recent) +{ + long timeout = libxl__get_domid_reuse_timeout(); + const char *name; + FILE *f; + struct timespec ts; + unsigned long sec; + unsigned int val; + int rc = ERROR_FAIL; + + name = GCSPRINTF("%s/domid-history", libxl__run_dir_path()); + f = fopen(name, "r"); + if (!f) { + if (errno != ENOENT) + LOGED(WARN, domid, "failed to open %s", name); + else + rc = 0; + + goto out; + } + + if (clock_gettime(CLOCK_MONOTONIC, &ts)) { + LOGED(ERROR, domid, "failed to get time"); + goto out; + } + + *recent = false; + while (libxl__read_recent(f, &sec, &val)) { + if (!libxl_domid_valid_guest(val)) + continue; /* Ignore invalid entries */ + + if (val == domid && ts.tv_sec - sec <= timeout) { + *recent = true; + break; + } + } + if (ferror(f)) { + LOGED(ERROR, domid, "failed to read from '%s'", name); + goto out; + } + + if (fclose(f) == EOF) { + LOGED(ERROR, domid, "failed to close '%s'", name); + f = NULL; + goto out; + } + f = NULL; + rc = 0; + +out: + if (f) fclose(f); + return rc; +} + static void devices_destroy_cb(libxl__egc *egc, libxl__devices_remove_state *drs, int rc) @@ -1331,6 +1533,8 @@ static void devices_destroy_cb(libxl__egc *egc, if (!ctx->xch) goto badchild; if (!dis->soft_reset) { + rc = libxl__mark_domid_recent(gc, domid); + if (rc) goto badchild; rc = xc_domain_destroy(ctx->xch, domid); } else { rc = xc_domain_pause(ctx->xch, domid); diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c index 211236dc99..bbd4c6cba9 100644 --- a/tools/libxl/libxl_internal.c +++ b/tools/libxl/libxl_internal.c @@ -504,6 +504,16 @@ libxl__flock *libxl__lock_domain_userdata(libxl__gc *gc, uint32_t domid) return lock; } +libxl__flock *libxl__lock_domid_history(libxl__gc *gc) +{ + const char *lockfile; + + lockfile = libxl__domid_history_path(gc, ".lock"); + if (!lockfile) return NULL; + + return libxl__lock_file(gc, lockfile); +} + int libxl__get_domain_configuration(libxl__gc *gc, uint32_t domid, libxl_domain_config *d_config) { diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h index dd3c08bc14..39de2d5910 100644 --- a/tools/libxl/libxl_internal.h +++ b/tools/libxl/libxl_internal.h @@ -4260,6 +4260,8 @@ _hidden void libxl__remus_teardown(libxl__egc *egc, _hidden void libxl__remus_restore_setup(libxl__egc *egc, libxl__domain_create_state *dcs); +_hidden char *libxl__domid_history_path(libxl__gc *gc, + const char *suffix); /* * Convenience macros. @@ -4658,6 +4660,7 @@ libxl__flock *libxl__lock_file(libxl__gc *gc, const char *filename); void libxl__unlock_file(libxl__flock *lock); libxl__flock *libxl__lock_domain_userdata(libxl__gc *gc, uint32_t domid); +libxl__flock *libxl__lock_domid_history(libxl__gc *gc); /* * Retrieve / store domain configuration from / to libxl private @@ -4796,6 +4799,17 @@ _hidden int libxl__domain_pvcontrol(libxl__egc *egc, libxl__xswait_state *pvcontrol, domid_t domid, const char *cmd); +/* + * Maximum number of seconds after desctruction then a domid remains + * 'recent'. Recent domids are not allowed to be re-used. This can be + * overidden, for debugging purposes, by the environment variable of the + * same name. + */ +#define LIBXL_DOMID_REUSE_TIMEOUT 60 + +/* Check whether a domid is recent */ +int libxl__is_domid_recent(libxl__gc *gc, uint32_t domid, bool *recent); + #endif /* -- 2.20.1 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel