[PATCH V9 36/46] chardev: cpr framework

[Steve Sistare <steven.sistare@oracle.com>]

Add QEMU_CHAR_FEATURE_CPR for devices that support cpr-exec by preserving
an open descriptor across exec.  Add the chardev reopen-on-cpr option for
devices that should be closed on cpr and reopened after exec.

Enable cpr for a chardev if it has QEMU_CHAR_FEATURE_CPR and reopen-on-cpr
is false.  Allow cpr-save if either QEMU_CHAR_FEATURE_CPR or reopen-on-cpr
is true for all chardevs in the configuration.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 chardev/char.c         | 49 +++++++++++++++++++++++++++++++++++++++++++++----
 include/chardev/char.h |  5 +++++
 qapi/char.json         |  7 ++++++-
 qemu-options.hx        | 26 ++++++++++++++++++++++----
 4 files changed, 78 insertions(+), 9 deletions(-)

diff --git a/chardev/char.c b/chardev/char.c
index 0169d8d..01755d7 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -36,6 +36,8 @@
 #include "qemu/help_option.h"
 #include "qemu/module.h"
 #include "qemu/option.h"
+#include "migration/cpr-state.h"
+#include "migration/blocker.h"
 #include "qemu/id.h"
 #include "qemu/coroutine.h"
 #include "qemu/yank.h"
@@ -236,26 +238,55 @@ int qemu_chr_add_client(Chardev *s, int fd)
 static void qemu_char_open(Chardev *chr, ChardevBackend *backend,
                            bool *be_opened, Error **errp)
 {
+    ERRP_GUARD();
+    g_autofree char *fdname = NULL;
+
     ChardevClass *cc = CHARDEV_GET_CLASS(chr);
     /* Any ChardevCommon member would work */
     ChardevCommon *common = backend ? backend->u.null.data : NULL;
+    bool has_logfile = (common && common->has_logfile);
+    bool has_feature_cpr;
 
-    if (common && common->has_logfile) {
+    if (has_logfile) {
         int flags = O_WRONLY;
+        fdname = g_strdup_printf("%s_log", chr->label);
         if (common->has_logappend &&
             common->logappend) {
             flags |= O_APPEND;
         } else {
             flags |= O_TRUNC;
         }
-        chr->logfd = qemu_create(common->logfile, flags, 0666, errp);
+        chr->logfd = cpr_find_fd(fdname, 0);
+        if (chr->logfd < 0) {
+            chr->logfd = qemu_create(common->logfile, flags, 0666, errp);
+        }
         if (chr->logfd < 0) {
             return;
         }
     }
 
+    chr->reopen_on_cpr = (common && common->reopen_on_cpr);
+
     if (cc->open) {
         cc->open(chr, backend, be_opened, errp);
+        if (*errp) {
+            return;
+        }
+    }
+
+    /* Evaluate this after the open method sets the feature */
+    has_feature_cpr = qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_CPR);
+    chr->cpr_enabled = !chr->reopen_on_cpr && has_feature_cpr;
+
+    if (!chr->reopen_on_cpr && !has_feature_cpr) {
+        chr->cpr_blocker = NULL;
+        error_setg(&chr->cpr_blocker,
+                "chardev %s -> %s does not allow cpr. See reopen-on-cpr.",
+                chr->label, chr->filename);
+        migrate_add_blockers(&chr->cpr_blocker, errp, MIG_MODE_CPR_EXEC, -1);
+
+    } else if (chr->cpr_enabled && has_logfile) {
+        cpr_resave_fd(fdname, 0, chr->logfd);
     }
 }
 
@@ -297,11 +328,16 @@ static void char_finalize(Object *obj)
     if (chr->be) {
         chr->be->chr = NULL;
     }
-    g_free(chr->filename);
-    g_free(chr->label);
     if (chr->logfd != -1) {
+        g_autofree char *fdname = g_strdup_printf("%s_log", chr->label);
+        if (chr->cpr_enabled) {
+            cpr_delete_fd(fdname, 0);
+        }
         close(chr->logfd);
     }
+    migrate_del_blocker(&chr->cpr_blocker);
+    g_free(chr->filename);
+    g_free(chr->label);
     qemu_mutex_destroy(&chr->chr_write_lock);
 }
 
@@ -501,6 +537,8 @@ void qemu_chr_parse_common(QemuOpts *opts, ChardevCommon *backend)
 
     backend->has_logappend = true;
     backend->logappend = qemu_opt_get_bool(opts, "logappend", false);
+
+    backend->reopen_on_cpr = qemu_opt_get_bool(opts, "reopen-on-cpr", false);
 }
 
 static const ChardevClass *char_get_class(const char *driver, Error **errp)
@@ -942,6 +980,9 @@ QemuOptsList qemu_chardev_opts = {
         },{
             .name = "abstract",
             .type = QEMU_OPT_BOOL,
+        },{
+            .name = "reopen-on-cpr",
+            .type = QEMU_OPT_BOOL,
 #endif
         },
         { /* end of list */ }
diff --git a/include/chardev/char.h b/include/chardev/char.h
index a319b5f..bbf2560 100644
--- a/include/chardev/char.h
+++ b/include/chardev/char.h
@@ -50,6 +50,8 @@ typedef enum {
     /* Whether the gcontext can be changed after calling
      * qemu_chr_be_update_read_handlers() */
     QEMU_CHAR_FEATURE_GCONTEXT,
+    /* Whether the device supports cpr */
+    QEMU_CHAR_FEATURE_CPR,
 
     QEMU_CHAR_FEATURE_LAST,
 } ChardevFeature;
@@ -67,6 +69,9 @@ struct Chardev {
     int be_open;
     /* used to coordinate the chardev-change special-case: */
     bool handover_yank_instance;
+    bool reopen_on_cpr;
+    bool cpr_enabled;
+    Error *cpr_blocker;
     GSource *gsource;
     GMainContext *gcontext;
     DECLARE_BITMAP(features, QEMU_CHAR_FEATURE_LAST);
diff --git a/qapi/char.json b/qapi/char.json
index 923dc50..0c3558e 100644
--- a/qapi/char.json
+++ b/qapi/char.json
@@ -204,12 +204,17 @@
 # @logfile: The name of a logfile to save output
 # @logappend: true to append instead of truncate
 #             (default to false to truncate)
+# @reopen-on-cpr: if true, close device's fd on cpr-save and reopen it after
+#                 cpr-exec. Set this to allow CPR on a device that does not
+#                 support QEMU_CHAR_FEATURE_CPR. defaults to false.
+#                 since 7.1.
 #
 # Since: 2.6
 ##
 { 'struct': 'ChardevCommon',
   'data': { '*logfile': 'str',
-            '*logappend': 'bool' } }
+            '*logappend': 'bool',
+            '*reopen-on-cpr': 'bool' } }
 
 ##
 # @ChardevFile:
diff --git a/qemu-options.hx b/qemu-options.hx
index 3ed9270..ea79afa 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3295,43 +3295,57 @@ DEFHEADING(Character device options:)
 
 DEF("chardev", HAS_ARG, QEMU_OPTION_chardev,
     "-chardev help\n"
-    "-chardev null,id=id[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "-chardev null,id=id[,mux=on|off][,logfile=PATH][,logappend=on|off][,reopen-on-cpr=on|off]\n"
     "-chardev socket,id=id[,host=host],port=port[,to=to][,ipv4=on|off][,ipv6=on|off][,nodelay=on|off]\n"
     "         [,server=on|off][,wait=on|off][,telnet=on|off][,websocket=on|off][,reconnect=seconds][,mux=on|off]\n"
-    "         [,logfile=PATH][,logappend=on|off][,tls-creds=ID][,tls-authz=ID] (tcp)\n"
+    "         [,logfile=PATH][,logappend=on|off][,tls-creds=ID][,tls-authz=ID][,reopen-on-cpr=on|off] (tcp)\n"
     "-chardev socket,id=id,path=path[,server=on|off][,wait=on|off][,telnet=on|off][,websocket=on|off][,reconnect=seconds]\n"
-    "         [,mux=on|off][,logfile=PATH][,logappend=on|off][,abstract=on|off][,tight=on|off] (unix)\n"
+    "         [,mux=on|off][,logfile=PATH][,logappend=on|off][,abstract=on|off][,tight=on|off][,reopen-on-cpr=on|off] (unix)\n"
     "-chardev udp,id=id[,host=host],port=port[,localaddr=localaddr]\n"
     "         [,localport=localport][,ipv4=on|off][,ipv6=on|off][,mux=on|off]\n"
-    "         [,logfile=PATH][,logappend=on|off]\n"
+    "         [,logfile=PATH][,logappend=on|off][,reopen-on-cpr=on|off]\n"
     "-chardev msmouse,id=id[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
     "-chardev vc,id=id[[,width=width][,height=height]][[,cols=cols][,rows=rows]]\n"
     "         [,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
     "-chardev ringbuf,id=id[,size=size][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
     "-chardev file,id=id,path=path[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
     "-chardev pipe,id=id,path=path[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
 #ifdef _WIN32
     "-chardev console,id=id[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
     "-chardev serial,id=id,path=path[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
 #else
     "-chardev pty,id=id[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
     "-chardev stdio,id=id[,mux=on|off][,signal=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
 #endif
 #ifdef CONFIG_BRLAPI
     "-chardev braille,id=id[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
 #endif
 #if defined(__linux__) || defined(__sun__) || defined(__FreeBSD__) \
         || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__)
     "-chardev serial,id=id,path=path[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
     "-chardev tty,id=id,path=path[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
 #endif
 #if defined(__linux__) || defined(__FreeBSD__) || defined(__DragonFly__)
     "-chardev parallel,id=id,path=path[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
     "-chardev parport,id=id,path=path[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
 #endif
 #if defined(CONFIG_SPICE)
     "-chardev spicevmc,id=id,name=name[,debug=debug][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
     "-chardev spiceport,id=id,name=name[,debug=debug][,logfile=PATH][,logappend=on|off]\n"
+    "         [,reopen-on-cpr=on|off]\n"
 #endif
     , QEMU_ARCH_ALL
 )
@@ -3406,6 +3420,10 @@ The general form of a character device option is:
     ``logappend`` option controls whether the log file will be truncated
     or appended to when opened.
 
+    Every backend supports the ``reopen-on-cpr`` option.  If on, the
+    devices's descriptor is closed during cpr save, and reopened after exec.
+    This is useful for devices that do not support cpr.
+
 The available backends are:
 
 ``-chardev null,id=id``
-- 
1.8.3.1