LXR busybox/shell/ash_remove_unnecessary_code_in_backquote

   1From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
   2Date: Thu, 19 Apr 2018 18:16:12 +0800
   3
   4> ash originally had support for omitting the fork when expanding a
   5> builtin in backquotes.  dash has gradually been removing this support,
   6> most recently in commit 66b614e29038e31745c4a5d296f64f8d64f5c377
   7> ("[EVAL] Remove unused EV_BACKCMD flag").
   8>
   9> Some traces still remain, however.  Remove:
  10>
  11> - the buf and nleft elements of the backcmd structure;
  12> - a misleading comment regarding handling of builtins.
  13>
  14> Signed-off-by: Ron Yorston <rmy@xxxxxxxxxxxx>
  15
  16Unfortunately we may need this at some point in the future due
  17to changes in POSIX.  So let's keep it around for now until we
  18get things such as `jobs -p` to work.
  19
  20*************************************
  21
  22From: Ron Yorston <rmy@xxxxxxxxxxxx>
  23Date: Thu, 19 Apr 2018 17:18:47 +0100
  24
  25>Unfortunately we may need this at some point in the future due
  26>to changes in POSIX.  So let's keep it around for now until we
  27>get things such as `jobs -p` to work.
  28
  29As you wish.
  30
  31Something even more trivial I noticed later:  the TRACE at the end of
  32expbackq incorrectly refers to the function as evalbackq.
  33
  34*************************************
  35
  36Date: Tue, 10 Apr 2018 13:23:35 +0100
  37From: Ron Yorston <rmy@pobox.com>
  38To: busybox@busybox.net
  39Subject: [PATCH] ash: remove unnecessary code in backquote expansion
  40
  41Some traces remain of ash's ancient support for omitting the fork when
  42expanding a builtin command in backquotes.
  43
  44Remove:
  45
  46- the buf and nleft elements of the backcmd structure;
  47- a misleading comment regarding handling of builtins.
  48
  49I've submitted a similar patch to dash.
  50
  51Signed-off-by: Ron Yorston <rmy@pobox.com>
  52---
  53 shell/ash.c | 37 +++++++++----------------------------
  54 1 file changed, 9 insertions(+), 28 deletions(-)
  55
  56diff --git a/shell/ash.c b/shell/ash.c
  57index 45c747dbc..6f1458722 100644
  58--- a/shell/ash.c
  59+++ b/shell/ash.c
  60@@ -6356,15 +6356,12 @@ exptilde(char *startp, char *p, int flags)
  61 }
  62 
  63 /*
  64- * Execute a command inside back quotes.  If it's a builtin command, we
  65- * want to save its output in a block obtained from malloc.  Otherwise
  66- * we fork off a subprocess and get the output of the command via a pipe.
  67- * Should be called with interrupts off.
  68+ * Execute a command inside back quotes.  We fork off a subprocess and
  69+ * get the output of the command via a pipe.  Should be called with
  70+ * interrupts off.
  71  */
  72 struct backcmd {                /* result of evalbackcmd */
  73        int fd;                 /* file descriptor to read from */
  74-       int nleft;              /* number of chars in buffer */
  75-       char *buf;              /* buffer */
  76        struct job *jp;         /* job structure for command */
  77 };
  78 
  79@@ -6394,8 +6391,6 @@ evalbackcmd(union node *n, struct backcmd *result)
  80        struct job *jp;
  81 
  82        result->fd = -1;
  83-       result->buf = NULL;
  84-       result->nleft = 0;
  85        result->jp = NULL;
  86        if (n == NULL) {
  87                goto out;
  88@@ -6432,8 +6427,7 @@ evalbackcmd(union node *n, struct backcmd *result)
  89        result->jp = jp;
  90 
  91  out:
  92-       TRACE(("evalbackcmd done: fd=%d buf=0x%x nleft=%d jp=0x%x\n",
  93-               result->fd, result->buf, result->nleft, result->jp));
  94+       TRACE(("evalbackcmd done: fd=%d jp=0x%x\n", result->fd, result->jp));
  95 }
  96 
  97 /*
  98@@ -6445,7 +6439,6 @@ expbackq(union node *cmd, int flag)
  99        struct backcmd in;
 100        int i;
 101        char buf[128];
 102-       char *p;
 103        char *dest;
 104        int startloc;
 105        int syntax = flag & EXP_QUOTED ? DQSYNTAX : BASESYNTAX;
 106@@ -6457,24 +6450,12 @@ expbackq(union node *cmd, int flag)
 107        evalbackcmd(cmd, &in);
 108        popstackmark(&smark);
 109 
 110-       p = in.buf;
 111-       i = in.nleft;
 112-       if (i == 0)
 113-               goto read;
 114-       for (;;) {
 115-               memtodest(p, i, syntax, flag & QUOTES_ESC);
 116- read:
 117-               if (in.fd < 0)
 118-                       break;
 119-               i = nonblock_immune_read(in.fd, buf, sizeof(buf));
 120-               TRACE(("expbackq: read returns %d\n", i));
 121-               if (i <= 0)
 122-                       break;
 123-               p = buf;
 124-       }
 125-
 126-       free(in.buf);
 127        if (in.fd >= 0) {
 128+               while ((i = nonblock_immune_read(in.fd, buf, sizeof(buf))) > 0) {
 129+                       TRACE(("expbackq: read returns %d\n", i));
 130+                       memtodest(buf, i, syntax, flag & QUOTES_ESC);
 131+               }
 132+
 133                close(in.fd);
 134                back_exitstatus = waitforjob(in.jp);
 135        }
 136