[PATCH] ash: add support for history buffer

[Dennis Groenen]

Ash writes to ~/.ash_history after every command, causing excessive
wear on devices which use a flash-based device as their storage medium
(i.e. one erase block cycle per command).
This patch allows you to set a temporary location where ash's history
will be saved until the shell is exited.

The patch is a bit hackish, but seems to do its job fine.

Signed-off-by: Dennis Groenen <tj.groenen at gmail.com>
---
 shell/ash.c |   51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 51 insertions(+), 0 deletions(-)

diff --git a/shell/ash.c b/shell/ash.c
index d48cd01..940dfe9 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -184,6 +184,24 @@
 //config:	  This option recreates the prompt string from the environment
 //config:	  variable each time it is displayed.
 //config:
+//config:config ASH_HIST_BUFFER
+//config:	bool "History buffer"
+//config:	default n
+//config:	depends on ASH && FEATURE_EDITING_SAVEHISTORY
+//config:	help
+//config:	  Allows you to set a temporary location for .ash_history.
+//config:	  History is saved to this custom location, and written out to
+//config:	  its default location (~/.ash_history) upon shell exit.
+//config:	  Useful to prevent wear on flash-based storage devices.
+//config:
+//config:config ASH_HIST_BUFFER_PATH
+//config:	string "History buffer location"
+//config:	default "/tmp"
+//config:	depends on ASH && ASH_HIST_BUFFER
+//config:	help
+//config:	  Directory which will be used to save the shell history until
+//config:	  ash is exited.
+//config:

 //applet:IF_ASH(APPLET(ash, BB_DIR_BIN, BB_SUID_DROP))
 //applet:IF_FEATURE_SH_IS_ASH(APPLET_ODDNAME(sh, ash, BB_DIR_BIN,
BB_SUID_DROP, sh))
@@ -12888,6 +12906,14 @@ exitshell(void)
 	char *p;
 	int status;

+#if ENABLE_ASH_HIST_BUFFER
+	const char *tmphistory = lookupvar("HISTFILE");
+	const char *storedhistory = lookupvar("STOREDHISTFILE");
+
+	if (access(tmphistory, R_OK) == 0)
+		copy_file(tmphistory, storedhistory, 11); /* 11 = force copy &
preserve permissions */
+#endif
+
 	status = exitstatus;
 	TRACE(("pid %d, exitshell(%d)\n", getpid(), status));
 	if (setjmp(loc.loc)) {
@@ -13151,9 +13177,34 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
 		if (!hp) {
 			hp = lookupvar("HOME");
 			if (hp) {
+#if ENABLE_ASH_HIST_BUFFER
+				char *tmphistory;
+				char *storedhistory;
+				const char *user = lookupvar("USER");
+
+				if (access(CONFIG_ASH_HIST_BUFFER_PATH, R_OK == -1))
+					bb_make_directory(xasprintf("%s", CONFIG_ASH_HIST_BUFFER_PATH),
01777, FILEUTILS_RECUR);
+
+				tmphistory = concat_path_file(CONFIG_ASH_HIST_BUFFER_PATH,
+					xasprintf(".ash_hist_%s", user));
+				storedhistory = concat_path_file(hp, ".ash_history");
+
+				/* Create ~/.ash_history if non-existant */
+				if (access(storedhistory, R_OK) == -1)
+					close(open(storedhistory, O_WRONLY | O_CREAT, 0644));
+				/* Copy stored history to buffer locaton if the latter is non-existant */
+				if (access(tmphistory, R_OK | W_OK) == -1)
+					copy_file(storedhistory, tmphistory, 11); /* 11 = force copy &
preserve permissions */
+
+				setvar("HISTFILE", tmphistory, 0);
+				setvar("STOREDHISTFILE", storedhistory, 0);
+				free(storedhistory);
+				free(tmphistory);
+#else
 				char *defhp = concat_path_file(hp, ".ash_history");
 				setvar("HISTFILE", defhp, 0);
 				free(defhp);
+#endif
 			}
 		}
 	}
-- 
1.7.6