shell: update HISTFILESIZE code to be actually useful

"HISTFILESIZE=0" in profile wasn't working as intended,
"unset HISTFILE" wasn't preventing creation of history files
Now:
HISTSIZE=n      allows to reduce in-memory history buffer
HISTFILESIZE=n  allows to reduce history file size (0: truncate it)
unset HISTFILE  allows to not save history file at all

function                                             old     new   delta
exitshell                                            138     194     +56
hush_exit                                             97     143     +46
save_history                                         266     296     +30
hush_main                                           1170    1186     +16
.rodata                                           105762  105771      +9
load_history                                         246     254      +8
size_from_HISTFILESIZE                                44      41      -3
read_line_input                                     2746    2712     -34
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 6/2 up/down: 165/-37)           Total: 128 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

3 files changed, 63 insertions, 11 deletions

diff --git a/shell/Config.src b/shell/Config.src
index 5efbf9995..5b3fe08f3 100644
--- a/shell/Config.src
+++ b/shell/Config.src
@@ -166,9 +166,10 @@ config FEATURE_SH_HISTFILESIZE
         default y
         depends on SHELL_ASH || SHELL_HUSH
         help
-        This option makes busybox shells to use $HISTFILESIZE variable
-        to set shell history size. Note that its max value is capped
-        by "History size" setting in library tuning section.
+        This option makes busybox shells to use $HISTSIZE and
+        $HISTFILESIZE variables to set shell history size.
+        Note that its max value is capped by "History size" setting
+        in library tuning section.
 
 config FEATURE_SH_EMBEDDED_SCRIPTS
         bool "Embed scripts in the binary"
diff --git a/shell/ash.c b/shell/ash.c
index 16eb88a7b..18344767a 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -14525,8 +14525,25 @@ exitshell(void)
         char *p;
 
 #if ENABLE_FEATURE_EDITING_SAVE_ON_EXIT
-        save_history(line_input_state); /* may be NULL */
+        if (line_input_state) {
+                const char *hp;
+# if ENABLE_FEATURE_SH_HISTFILESIZE
+// in bash:
+// HISTFILESIZE controls the on-disk history file size (in lines, 0=no history):
+// "When this variable is assigned a value, the history file is truncated, if necessary"
+// but we do it only at exit, not on assignment:
+                /* Use HISTFILESIZE to limit file size */
+                hp = lookupvar("HISTFILESIZE");
+                if (hp)
+                        line_input_state->max_history = size_from_HISTFILESIZE(hp);
+# endif
+                /* HISTFILE: "If unset, the command history is not saved when a shell exits." */
+                hp = lookupvar("HISTFILE");
+                line_input_state->hist_file = hp;
+                save_history(line_input_state); /* no-op if hist_file is NULL */
+        }
 #endif
+
         savestatus = exitstatus;
         TRACE(("pid %d, exitshell(%d)\n", getpid(), savestatus));
         if (setjmp(loc.loc))
@@ -14867,7 +14884,12 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
                         if (hp)
                                 line_input_state->hist_file = xstrdup(hp);
 # if ENABLE_FEATURE_SH_HISTFILESIZE
-                        hp = lookupvar("HISTFILESIZE");
+                        hp = lookupvar("HISTSIZE");
+                        /* Using HISTFILESIZE above to limit max_history would be WRONG:
+                         * users may set HISTFILESIZE=0 in their profile scripts
+                         * to prevent _saving_ of history files, but still want to have
+                         * non-zero history limit for in-memory list.
+                         */
                         line_input_state->max_history = size_from_HISTFILESIZE(hp);
 # endif
                 }
diff --git a/shell/hush.c b/shell/hush.c
index 70b730f67..68aca53a3 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -2099,11 +2099,29 @@ static sighandler_t pick_sighandler(unsigned sig)
         return handler;
 }
 
+static const char* FAST_FUNC get_local_var_value(const char *name);
+
 /* Restores tty foreground process group, and exits. */
 static void hush_exit(int exitcode)
 {
 #if ENABLE_FEATURE_EDITING_SAVE_ON_EXIT
-        save_history(G.line_input_state); /* may be NULL */
+        if (G.line_input_state) {
+                const char *hp;
+# if ENABLE_FEATURE_SH_HISTFILESIZE
+// in bash:
+// HISTFILESIZE controls the on-disk history file size (in lines, 0=no history):
+// "When this variable is assigned a value, the history file is truncated, if necessary"
+// but we do it only at exit, not on every assignment:
+                /* Use HISTFILESIZE to limit file size */
+                hp = get_local_var_value("HISTFILESIZE");
+                if (hp)
+                        G.line_input_state->max_history = size_from_HISTFILESIZE(hp);
+# endif
+                /* HISTFILE: "If unset, the command history is not saved when a shell exits." */
+                hp = get_local_var_value("HISTFILE");
+                G.line_input_state->hist_file = hp;
+                save_history(G.line_input_state); /* no-op if hist_file is NULL */
+        }
 #endif
 
         fflush_all();
@@ -10427,7 +10445,7 @@ int hush_main(int argc, char **argv)
         if (!get_local_var_value("PATH"))
                 set_local_var_from_halves("PATH", bb_default_root_path);
 
-        /* PS1/PS2 are set later, if we determine that we are interactive */
+        /* PS1/PS2/HISTFILE are set later, if we determine that we are interactive */
 
         /* bash also exports SHLVL and _,
          * and sets (but doesn't export) the following variables:
@@ -10449,7 +10467,6 @@ int hush_main(int argc, char **argv)
          * BASH_SOURCE=()
          * DIRSTACK=()
          * PIPESTATUS=([0]="0")
-         * HISTFILE=/<xxx>/.bash_history
          * HISTFILESIZE=500
          * HISTSIZE=500
          * MAILCHECK=60
@@ -10809,18 +10826,30 @@ int hush_main(int argc, char **argv)
                         const char *hp = get_local_var_value("HISTFILE");
                         if (!hp) {
                                 hp = get_local_var_value("HOME");
-                                if (hp)
+                                if (hp) {
                                         hp = concat_path_file(hp, ".hush_history");
+                                        /* Make HISTFILE set on exit (else history won't be saved) */
+                                        set_local_var_from_halves("HISTFILE", hp);
+                                }
                         } else {
                                 hp = xstrdup(hp);
                         }
                         if (hp) {
                                 G.line_input_state->hist_file = hp;
-                                //set_local_var(xasprintf("HISTFILE=%s", ...));
                         }
 #  if ENABLE_FEATURE_SH_HISTFILESIZE
-                        hp = get_local_var_value("HISTFILESIZE");
+                        hp = get_local_var_value("HISTSIZE");
+                        /* Using HISTFILESIZE above to limit max_history would be WRONG:
+                         * users may set HISTFILESIZE=0 in their profile scripts
+                         * to prevent _saving_ of history files, but still want to have
+                         * non-zero history limit for in-memory list.
+                         */
+// in bash, runtime history size is controlled by HISTSIZE (0=no history),
+// HISTFILESIZE controls on-disk history file size (in lines, 0=no history):
                         G.line_input_state->max_history = size_from_HISTFILESIZE(hp);
+// HISTFILESIZE: "The shell sets the default value to the value of HISTSIZE after reading any startup files."
+// HISTSIZE: "The shell sets the default value to 500 after reading any startup files."
+// (meaning: if the value wasn't set after startup files, the default value is set as described above)
 #  endif
                 }
 # endif