Fix dbgmsg printing in ztest and zdb

This patch resolves a problem where the -G option in both zdb and
ztest would cause the code to call __dprintf() to print zfs_dbgmsg
output. This function was not properly wired to add messages to the
dbgmsg log as it is in userspace and so the messages were simply
dropped. This patch also tries to add some degree of distinction to
dprintf() (which now prints directly to stdout) and zfs_dbgmsg()
(which adds messages to an internal list that can be dumped with
zfs_dbgmsg_print()).

In addition, this patch corrects an issue where ztest used a global
variable to decide whether to dump the dbgmsg buffer on a crash.
This did not work because ztest spins up more instances of itself
using execv(), which did not copy the global variable to the new
process. The option has been moved to the ztest_shared_opts_t
which already exists for interprocess communication.

This patch also changes zfs_dbgmsg_print() to use write() calls
instead of printf() so that it will not fail when used in a signal
handler.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Serapheim Dimitropoulos <[email protected]>
Reviewed-by: Matthew Ahrens <[email protected]>
Signed-off-by: Tom Caputi <[email protected]>
Closes #8010

1 files changed, 34 insertions, 12 deletions

diff --git a/module/zfs/zfs_debug.c b/module/zfs/zfs_debug.c
index b5f93fd9b..62c59e020 100644
--- a/module/zfs/zfs_debug.c
+++ b/module/zfs/zfs_debug.c
@@ -124,11 +124,10 @@ __set_error(const char *file, const char *func, int line, int err)
 	 * $ echo 512 >/sys/module/zfs/parameters/zfs_flags
 	 */
 	if (zfs_flags & ZFS_DEBUG_SET_ERROR)
-		__dprintf(file, func, line, "error %lu", err);
+		__dprintf(B_FALSE, file, func, line, "error %lu", err);
 }
 
-#ifdef _KERNEL
-static void
+void
 __zfs_dbgmsg(char *buf)
 {
 	int size = sizeof (zfs_dbgmsg_t) + strlen(buf);
@@ -144,8 +143,11 @@ __zfs_dbgmsg(char *buf)
 	mutex_exit(&zfs_dbgmsgs.pl_lock);
 }
 
+#ifdef _KERNEL
+
 void
-__dprintf(const char *file, const char *func, int line, const char *fmt, ...)
+__dprintf(boolean_t dprint, const char *file, const char *func,
+    int line, const char *fmt, ...)
 {
 	const char *newfile;
 	va_list adx;
@@ -153,6 +155,7 @@ __dprintf(const char *file, const char *func, int line, const char *fmt, ...)
 	char *buf;
 	char *nl;
 	int i;
+	char *prefix = (dprint) ? "dprintf: " : "";
 
 	size = 1024;
 	buf = kmem_alloc(size, KM_SLEEP);
@@ -167,7 +170,7 @@ __dprintf(const char *file, const char *func, int line, const char *fmt, ...)
 		newfile = file;
 	}
 
-	i = snprintf(buf, size, "%s:%d:%s(): ", newfile, line, func);
+	i = snprintf(buf, size, "%s%s:%d:%s(): ", prefix, newfile, line, func);
 
 	if (i < size) {
 		va_start(adx, fmt);
@@ -176,11 +179,13 @@ __dprintf(const char *file, const char *func, int line, const char *fmt, ...)
 	}
 
 	/*
-	 * Get rid of trailing newline.
+	 * Get rid of trailing newline for dprintf logs.
 	 */
-	nl = strrchr(buf, '\n');
-	if (nl != NULL)
-		*nl = '\0';
+	if (dprint && buf[0] != '\0') {
+		nl = &buf[strlen(buf) - 1];
+		if (*nl == '\n')
+			*nl = '\0';
+	}
 
 	/*
 	 * To get this data enable the zfs__dprintf trace point as shown:
@@ -212,11 +217,28 @@ __dprintf(const char *file, const char *func, int line, const char *fmt, ...)
 void
 zfs_dbgmsg_print(const char *tag)
 {
-	(void) printf("ZFS_DBGMSG(%s):\n", tag);
+	ssize_t ret __attribute__((unused));
+
+	/*
+	 * We use write() in this function instead of printf()
+	 * so it is safe to call from a signal handler.
+	 */
+	ret = write(STDOUT_FILENO, "ZFS_DBGMSG(", 11);
+	ret = write(STDOUT_FILENO, tag, strlen(tag));
+	ret = write(STDOUT_FILENO, ") START:\n", 9);
+
 	mutex_enter(&zfs_dbgmsgs.pl_lock);
 	for (zfs_dbgmsg_t *zdm = list_head(&zfs_dbgmsgs.pl_list); zdm != NULL;
-	    zdm = list_next(&zfs_dbgmsgs.pl_list, zdm))
-		(void) printf("%s\n", zdm->zdm_msg);
+	    zdm = list_next(&zfs_dbgmsgs.pl_list, zdm)) {
+		ret = write(STDOUT_FILENO, zdm->zdm_msg,
+		    strlen(zdm->zdm_msg));
+		ret = write(STDOUT_FILENO, "\n", 1);
+	}
+
+	ret = write(STDOUT_FILENO, "ZFS_DBGMSG(", 11);
+	ret = write(STDOUT_FILENO, tag, strlen(tag));
+	ret = write(STDOUT_FILENO, ") END\n", 6);
+
 	mutex_exit(&zfs_dbgmsgs.pl_lock);
 }
 #endif /* _KERNEL */