confile: add lxc.console.size

lxc.console.size regulates the size of the console log file. This is intended
to replace lxc.console.buffer.logfile. The current semantics are:

- if lxc.console.size is not set:
  - no limit is placed on the size of the log file
- if lxc.console.size is set:
  - if lxc.console.rotate is set and the next write would exceed the limit:
    - write as much as possible into the old log file
    - rotate the log file
    - write as much as posible into the new log file
    - discard remaining bytes (scenario shouldn't be possible in normal
      circumstances)
  - if lxc.console.rotate is not set and the next write would exceed the limit:
    - keep overwriting the current log file

To make the log file a mirror of the in-memory ringbuffer simply set:
lxc.console.buffer.size == lxc.console.size.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

doc/lxc.container.conf.sgml.in

@@ -832,6 +832,34 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
           </listitem>
         </varlistentry>
 
+        <varlistentry>
+          <term>
+            <option>lxc.console.size</option>
+          </term>
+          <listitem>
+            <para>
+            Setting this option instructs liblxc to place a limit on the size of
+            the console log file specified in
+            <option>lxc.console.logfile</option>. Note that size of the log file
+            must be at least as big as a standard page size. When passed a value
+            smaller than a single page size liblxc will set the size of log file
+            to a single page size. A page size is usually 4kB.
+
+            The keyword 'auto' will cause liblxc to place a limit of 128kB on
+            the log file.
+
+            When manually specifying a size for the log file the value should
+            be a power of 2 when converted to bytes. Valid size prefixes are
+            'kB', 'MB', 'GB'. (Note that all conversions are based on multiples
+            of 1024. That means 'kb' == 'KiB', 'MB' == 'MiB', 'GB' == 'GiB'.)
+
+            If users want to mirror the console ringbuffer on disk they should set
+            <option>lxc.console.size</option> equal to
+            <option>lxc.console.buffer.size</option>.
+            </para>
+          </listitem>
+        </varlistentry>
+
         <varlistentry>
           <term>
             <option>lxc.console.buffer.logfile</option>

src/lxc/commands.c

@@ -1003,10 +1003,6 @@ static int lxc_cmd_console_log_callback(int fd, struct lxc_cmd_req *req,
 
 	rsp.ret = 0;
 	if (log->clear) {
-		int ret;
-		size_t len;
-		char *tmp;
-
 		/* clear the ringbuffer */
 		lxc_ringbuf_clear(buf);
 
@@ -1030,30 +1026,7 @@ static int lxc_cmd_console_log_callback(int fd, struct lxc_cmd_req *req,
 			}
 		}
 
-		/* rotate the console log file */
+		rsp.ret = lxc_console_rotate_log_file(console);
-		if (!console->log_path || console->log_rotate == 0)
-			goto out;
-
-		/* be very certain things are kosher */
-		rsp.ret = -EBADF;
-		if (console->log_fd < 0)
-			goto out;
-
-		len = strlen(console->log_path) + sizeof(".1");
-		tmp = alloca(len);
-
-		rsp.ret = -EFBIG;
-		ret = snprintf(tmp, len, "%s.1", console->log_path);
-		if (ret < 0 || (size_t)ret >= len)
-			goto out;
-
-		close(console->log_fd);
-		console->log_fd = -1;
-		rsp.ret = lxc_unpriv(rename(console->log_path, tmp));
-		if (rsp.ret < 0)
-			goto out;
-
-		rsp.ret = lxc_console_create_log_file(console);
 	} else if (rsp.datalen > 0) {
 		lxc_ringbuf_move_read_addr(buf, rsp.datalen);
 	}

src/lxc/conf.c

@@ -2614,6 +2614,7 @@ struct lxc_conf *lxc_conf_init(void)
 	new->console.buffer_size = 0;
 	new->console.log_path = NULL;
 	new->console.log_fd = -1;
+	new->console.log_size = 0;
 	new->console.path = NULL;
 	new->console.peer = -1;
 	new->console.peerpty.busy = -1;

src/lxc/conf.h

@@ -171,12 +171,24 @@ struct lxc_console {
 	struct lxc_pty_info peerpty;
 	struct lxc_epoll_descr *descr;
 	char *path;
-	char *log_path;
-	int log_fd;
-	unsigned int log_rotate;
 	char name[MAXPATHLEN];
 	struct termios *tios;
 	struct lxc_tty_state *tty_state;
+
+	struct /* lxc_console_log */ {
+		/* size of the log file */
+		uint64_t log_size;
+
+		/* path to the log file */
+		char *log_path;
+
+		/* fd to the log file */
+		int log_fd;
+
+		/* whether the log file will be rotated */
+		unsigned int log_rotate;
+	};
+
 	struct /* lxc_console_ringbuf */ {
 		/* size of the ringbuffer */
 		uint64_t buffer_size;

src/lxc/confile.c

@@ -82,11 +82,12 @@ lxc_config_define(cap_keep);
 lxc_config_define(cgroup_controller);
 lxc_config_define(cgroup2_controller);
 lxc_config_define(cgroup_dir);
-lxc_config_define(console_logfile);
-lxc_config_define(console_rotate);
 lxc_config_define(console_buffer_logfile);
 lxc_config_define(console_buffer_size);
+lxc_config_define(console_logfile);
 lxc_config_define(console_path);
+lxc_config_define(console_rotate);
+lxc_config_define(console_size);
 lxc_config_define(environment);
 lxc_config_define(ephemeral);
 lxc_config_define(execute_cmd);
@@ -160,6 +161,7 @@ static struct lxc_config_t config[] = {
 	{ "lxc.console.logfile",           set_config_console_logfile,             get_config_console_logfile,             clr_config_console_logfile,           },
 	{ "lxc.console.path",              set_config_console_path,                get_config_console_path,                clr_config_console_path,              },
 	{ "lxc.console.rotate",            set_config_console_rotate,              get_config_console_rotate,              clr_config_console_rotate,            },
+	{ "lxc.console.size",              set_config_console_size,                get_config_console_size,                clr_config_console_size,              },
 	{ "lxc.environment",               set_config_environment,                 get_config_environment,                 clr_config_environment,               },
 	{ "lxc.ephemeral",                 set_config_ephemeral,                   get_config_ephemeral,                   clr_config_ephemeral,                 },
 	{ "lxc.execute.cmd",               set_config_execute_cmd,                 get_config_execute_cmd,                 clr_config_execute_cmd,               },
@@ -1961,6 +1963,53 @@ static int set_config_console_buffer_size(const char *key, const char *value,
 	return 0;
 }
 
+static int set_config_console_size(const char *key, const char *value,
+				   struct lxc_conf *lxc_conf, void *data)
+{
+	int ret;
+	int64_t size;
+	uint64_t log_size, pgsz;
+
+	if (lxc_config_value_empty(value)) {
+		lxc_conf->console.log_size = 0;
+		return 0;
+	}
+
+	/* If the user specified "auto" the default log size is 2^17 = 128 Kib */
+	if (!strcmp(value, "auto")) {
+		lxc_conf->console.log_size = 1 << 17;
+		return 0;
+	}
+
+	ret = parse_byte_size_string(value, &size);
+	if (ret < 0)
+		return -1;
+
+	if (size < 0)
+		return -EINVAL;
+
+	/* must be at least a page size */
+	pgsz = lxc_getpagesize();
+	if ((uint64_t)size < pgsz) {
+		NOTICE("Requested ringbuffer size for the console is %" PRId64
+		       " but must be at least %" PRId64
+		       " bytes. Setting ringbuffer size to %" PRId64 " bytes",
+		       size, pgsz, pgsz);
+		size = pgsz;
+	}
+
+	log_size = lxc_find_next_power2((uint64_t)size);
+	if (log_size == 0)
+		return -EINVAL;
+
+	if (log_size != size)
+		NOTICE("Passed size was not a power of 2. Rounding log size to "
+		       "next power of two: %" PRIu64 " bytes", log_size);
+
+	lxc_conf->console.log_size = log_size;
+	return 0;
+}
+
 static int set_config_console_buffer_logfile(const char *key, const char *value,
 					     struct lxc_conf *lxc_conf,
 					     void *data)
@@ -3298,6 +3347,13 @@ static int get_config_console_buffer_size(const char *key, char *retv,
 	return lxc_get_conf_uint64(c, retv, inlen, c->console.buffer_size);
 }
 
+static int get_config_console_size(const char *key, char *retv, int inlen,
+				   struct lxc_conf *c, void *data)
+{
+	return lxc_get_conf_uint64(c, retv, inlen, c->console.log_size);
+}
+
+
 static int get_config_console_buffer_logfile(const char *key, char *retv,
 					     int inlen, struct lxc_conf *c,
 					     void *data)
@@ -3840,6 +3896,13 @@ static inline int clr_config_console_buffer_size(const char *key,
 	return 0;
 }
 
+static inline int clr_config_console_size(const char *key, struct lxc_conf *c,
+					  void *data)
+{
+	c->console.log_size = 0;
+	return 0;
+}
+
 static inline int clr_config_console_buffer_logfile(const char *key,
 						    struct lxc_conf *c,
 						    void *data)

src/lxc/console.c

@@ -204,6 +204,152 @@ void lxc_console_signal_fini(struct lxc_tty_state *ts)
 	free(ts);
 }
 
+static int lxc_console_truncate_log_file(struct lxc_console *console)
+{
+	/* be very certain things are kosher */
+	if (!console->log_path || console->log_fd < 0)
+		return -EBADF;
+
+	return lxc_unpriv(ftruncate(console->log_fd, 0));
+}
+
+static int lxc_console_rotate_log_file(struct lxc_console *console)
+{
+	int ret;
+	size_t len;
+	char *tmp;
+
+	/* rotate the console log file */
+	if (!console->log_path || console->log_rotate == 0)
+		return -EOPNOTSUPP;
+
+	/* be very certain things are kosher */
+	if (console->log_fd < 0)
+		return -EBADF;
+
+	len = strlen(console->log_path) + sizeof(".1");
+	tmp = alloca(len);
+
+	ret = snprintf(tmp, len, "%s.1", console->log_path);
+	if (ret < 0 || (size_t)ret >= len)
+		return -EFBIG;
+
+	close(console->log_fd);
+	console->log_fd = -1;
+	ret = lxc_unpriv(rename(console->log_path, tmp));
+	if (ret < 0)
+		return ret;
+
+	return lxc_console_create_log_file(console);
+}
+
+static int lxc_console_write_log_file(struct lxc_console *console, char *buf,
+				      int bytes_read)
+{
+	int ret;
+	int64_t space_left = -1;
+	struct stat st;
+
+	if (console->log_fd < 0)
+		return 0;
+
+	/* A log size <= 0 means that there's no limit on the size of the log
+         * file at which point we simply ignore whether the log is supposed to
+	 * be rotated or not.
+	 */
+	if (console->log_size <= 0)
+		return lxc_write_nointr(console->log_fd, buf, bytes_read);
+
+	/* Get current size of the log file. */
+	ret = fstat(console->log_fd, &st);
+	if (ret < 0) {
+		SYSERROR("Failed to stat the console log file descriptor");
+		return -1;
+	}
+
+	/* handle non-regular files */
+	if ((st.st_mode & S_IFMT) != S_IFREG) {
+		/* This isn't a regular file. so rotating the file seems a
+		 * dangerous thing to do, size limits are also very
+		 * questionable. Let's not risk anything and tell the user that
+		 * he's requesting us to do weird stuff.
+		 */
+		if (console->log_rotate > 0 || console->log_size > 0)
+			return -EINVAL;
+
+		/* I mean, sure log wherever you want to. */
+		return lxc_write_nointr(console->log_fd, buf, bytes_read);
+	}
+
+	/* check how much space we have left */
+	space_left = console->log_size - st.st_size;
+
+	/* User doesn't want to rotate the log file and there's no more space
+	 * left so simply truncate it.
+	 */
+	if (space_left <= 0 && console->log_rotate <= 0) {
+		ret = lxc_console_truncate_log_file(console);
+		if (ret < 0)
+			return ret;
+
+		if (bytes_read <= console->log_size)
+			return lxc_write_nointr(console->log_fd, buf, bytes_read);
+
+		/* Write as much as we can into the buffer and loose the rest. */
+		return lxc_write_nointr(console->log_fd, buf, console->log_size);
+	}
+
+	/* There's enough space left. */
+	if (bytes_read <= space_left)
+		return lxc_write_nointr(console->log_fd, buf, bytes_read);
+
+	/* There's not enough space left but at least write as much as we can
+	 * into the old log file.
+	 */
+	ret = lxc_write_nointr(console->log_fd, buf, space_left);
+	if (ret < 0)
+		return -1;
+
+	/* Calculate how many bytes we still need to write. */
+	bytes_read -= space_left;
+
+	/* There be more to write but we aren't instructed to rotate the log
+	 * file so simply return. There's no error on our side here.
+	 */
+	if (console->log_rotate > 0)
+		ret = lxc_console_rotate_log_file(console);
+	else
+		ret = lxc_console_truncate_log_file(console);
+	if (ret < 0)
+		return ret;
+
+	if (console->log_size < bytes_read) {
+		/* Well, this is unfortunate because it means that there is more
+		 * to write than the user has granted us space. There are
+		 * multiple ways to handle this but let's use the simplest one:
+		 * write as much as we can, tell the user that there was more
+		 * stuff to write and move on.
+		 * Note that this scenario shouldn't actually happen with the
+		 * standard pty-based console that LXC allocates since it will
+		 * be switched into raw mode. In raw mode only 1 byte at a time
+		 * should be read and written.
+		 */
+		WARN("Size of console log file is smaller than the bytes to write");
+		ret = lxc_write_nointr(console->log_fd, buf, console->log_size);
+		if (ret < 0)
+			return -1;
+		bytes_read -= ret;
+		return bytes_read;
+	}
+
+	/* Yay, we made it. */
+	ret = lxc_write_nointr(console->log_fd, buf, bytes_read);
+	if (ret < 0)
+		return -1;
+	bytes_read -= ret;
+	return bytes_read;
+}
+
 int lxc_console_cb_con(int fd, uint32_t events, void *data,
 		       struct lxc_epoll_descr *descr)
 {
@@ -245,9 +391,9 @@ int lxc_console_cb_con(int fd, uint32_t events, void *data,
 		if (console->buffer_size > 0)
 			w_rbuf = lxc_ringbuf_write(&console->ringbuf, buf, r);
 
-		/* write to console log */
+		if (console->log_fd > 0)
-		if (console->log_fd >= 0)
+			w_log = lxc_console_write_log_file(console, buf, r);
-			w_log = lxc_write_nointr(console->log_fd, buf, r);
+
 	}
 
 	if (w != r)