commit 2b91953273eb7c9ebd5ba4d38e4fde73d78cb147
Author: Kyle Evans <kevans@FreeBSD.org>
Date:   Wed Feb 17 13:34:28 2021 -0600

    grep: only read devices named on cmdline by default
    
    Assume a default of "read if explicitly mentioned" rather than "read"
    for -D. In particular, recursing into /dev will no longer get stuck on
    a tty, but one can still grep /dev/random.

:100644 100644 338af7e6d45 3da48cbcbc7 M	usr.bin/grep/grep.1
:100644 100644 166d3451774 a8d65930c71 M	usr.bin/grep/grep.c
:100644 100644 62e82c7f56b 0777760ab23 M	usr.bin/grep/grep.h
:100644 100644 a2520e24de8 9f191689cc5 M	usr.bin/grep/util.c

diff --git a/usr.bin/grep/grep.1 b/usr.bin/grep/grep.1
index 338af7e6d45..3da48cbcbc7 100644
--- a/usr.bin/grep/grep.1
+++ b/usr.bin/grep/grep.1
@@ -30,7 +30,7 @@
 .\"
 .\"	@(#)grep.1	8.3 (Berkeley) 4/18/94
 .\"
-.Dd February 4, 2021
+.Dd February 17, 2021
 .Dt GREP 1
 .Os
 .Sh NAME
@@ -162,6 +162,10 @@ If the
 is set to
 .Dq Cm skip ,
 devices are silently skipped.
+Note that the default
+.Dq Cm read
+operates differently in recursive mode, as the default behavior is to skip
+reading devices that were not explicitly listed as arguments.
 .It Fl d Ar action , Fl Fl directories= Ns Ar action
 Specify the demanded
 .Ar action
diff --git a/usr.bin/grep/grep.c b/usr.bin/grep/grep.c
index 166d3451774..a8d65930c71 100644
--- a/usr.bin/grep/grep.c
+++ b/usr.bin/grep/grep.c
@@ -113,7 +113,7 @@ const char *color;	/* --color */
 int	 grepbehave = GREP_BASIC;	/* -EFGP: type of the regex */
 int	 binbehave = BINFILE_BIN;	/* -aIU: handling of binary files */
 int	 filebehave = FILE_STDIO;
-int	 devbehave = DEV_READ;		/* -D: handling of devices */
+int	 devbehave = DEV_READ_NAMED;	/* -D: handling of devices */
 int	 dirbehave = DIR_READ;		/* -dRr: handling of directories */
 int	 linkbehave = LINK_READ;	/* -OpS: handling of symlinks */
 
@@ -703,7 +703,7 @@ main(int argc, char *argv[])
 	initqueue();
 
 	if (aargc == 0 && dirbehave != DIR_RECURSE)
-		exit(!procfile("-"));
+		exit(!procfile("-", 0));
 
 	if (dirbehave == DIR_RECURSE)
 		matched = grep_tree(aargv);
@@ -711,7 +711,7 @@ main(int argc, char *argv[])
 		for (matched = false; aargc--; ++aargv) {
 			if ((finclude || fexclude) && !file_matching(*aargv))
 				continue;
-			if (procfile(*aargv))
+			if (procfile(*aargv, 0))
 				matched = true;
 		}
 
diff --git a/usr.bin/grep/grep.h b/usr.bin/grep/grep.h
index 62e82c7f56b..0777760ab23 100644
--- a/usr.bin/grep/grep.h
+++ b/usr.bin/grep/grep.h
@@ -61,8 +61,9 @@ extern const char		*errstr[];
 #define	DIR_SKIP	1
 #define	DIR_RECURSE	2
 
-#define	DEV_READ	0
-#define	DEV_SKIP	1
+#define	DEV_READ_NAMED	0
+#define	DEV_READ	1
+#define	DEV_SKIP	2
 
 #define	LINK_READ	0
 #define	LINK_EXPLICIT	1
@@ -140,7 +141,7 @@ extern char	 re_error[RE_ERROR_BUF + 1];	/* Seems big enough */
 
 /* util.c */
 bool	 file_matching(const char *fname);
-bool	 procfile(const char *fn);
+bool	 procfile(const char *fn, long depth);
 bool	 grep_tree(char **argv);
 void	*grep_malloc(size_t size);
 void	*grep_calloc(size_t nmemb, size_t size);
diff --git a/usr.bin/grep/util.c b/usr.bin/grep/util.c
index a2520e24de8..9f191689cc5 100644
--- a/usr.bin/grep/util.c
+++ b/usr.bin/grep/util.c
@@ -182,7 +182,7 @@ grep_tree(char **argv)
 			if (fexclude || finclude)
 				ok &= file_matching(p->fts_path);
 
-			if (ok && procfile(p->fts_path))
+			if (ok && procfile(p->fts_path, p->fts_level))
 				matched = true;
 			break;
 		}
@@ -288,7 +288,7 @@ procmatches(struct mprintc *mc, struct parsec *pc, bool matched)
  * passing the lines to procline().
  */
 bool
-procfile(const char *fn)
+procfile(const char *fn, long depth)
 {
 	struct parsec pc;
 	struct mprintc mc;
@@ -307,9 +307,13 @@ procfile(const char *fn)
 			s = sb.st_mode & S_IFMT;
 			if (dirbehave == DIR_SKIP && s == S_IFDIR)
 				return (false);
-			if (devbehave == DEV_SKIP && (s == S_IFIFO ||
-			    s == S_IFCHR || s == S_IFBLK || s == S_IFSOCK))
-				return (false);
+			if (s == S_IFIFO || s == S_IFCHR || s == S_IFBLK ||
+			    s == S_IFSOCK) {
+				if (devbehave == DEV_SKIP)
+					return (false);
+				if (devbehave == DEV_READ_NAMED && depth != 0)
+					return (false);
+			}
 		}
 		f = grep_open(fn);
 	}