[rfc v3][4/6] Readlink as file I/O target operation

["Ulrich Weigand" <uweigand at de dot ibm dot com>]

ChangeLog:

	* configure.ac [AC_CHECK_FUNCS]: Check for readlink.
	* config.in, configure: Regenerate.

	* target.h (struct target_ops): Add to_fileio_readlink.
	(target_fileio_readlink): Add prototype.
	* target.c (target_fileio_readlink): New function.

	* inf-child.c: Conditionally include <sys/param.h>.
	(inf_child_fileio_readlink): New function.
	(inf_child_target): Install it.

	* remote.c (PACKET_vFile_readlink): New enum value.
	(remote_hostio_readlink): New function.
	(init_remote_ops): Install it.
	(_initialize_remote): Handle vFile:readlink packet type.

doc/ChangeLog:

        * gdb.texinfo (Remote Configuration): Document
	"set remote hostio-readlink-packet" command.
	(General Query Packets): Document vFile:readlink packet.

gdbserver/ChangeLog:

	* hostio.c (handle_readlink): New function.
	(handle_vFile): Call it to handle "vFile:readlink" packets.


Index: gdb-head/gdb/gdbserver/hostio.c
===================================================================
--- gdb-head.orig/gdb/gdbserver/hostio.c	2012-01-19 10:35:58.000000000 +0100
+++ gdb-head/gdb/gdbserver/hostio.c	2012-01-19 10:40:27.000000000 +0100
@@ -456,6 +456,37 @@ handle_unlink (char *own_buf)
   hostio_reply (own_buf, ret);
 }
 
+static void
+handle_readlink (char *own_buf, int *new_packet_len)
+{
+  char filename[PATH_MAX], linkname[PATH_MAX];
+  char *p;
+  int ret, bytes_sent;
+
+  p = own_buf + strlen ("vFile:readlink:");
+
+  if (require_filename (&p, filename)
+      || require_end (p))
+    {
+      hostio_packet_error (own_buf);
+      return;
+    }
+
+  ret = readlink (filename, linkname, sizeof linkname);
+  if (ret == -1)
+    {
+      hostio_error (own_buf);
+      return;
+    }
+
+  bytes_sent = hostio_reply_with_data (own_buf, linkname, ret, new_packet_len);
+
+  /* If the response does not fit into a single packet, do not attempt
+     to return a partial response, but simply fail.  */
+  if (bytes_sent < ret)
+    sprintf (own_buf, "F-1,%x", FILEIO_ENAMETOOLONG);
+}
+
 /* Handle all the 'F' file transfer packets.  */
 
 int
@@ -471,6 +502,8 @@ handle_vFile (char *own_buf, int packet_
     handle_close (own_buf);
   else if (strncmp (own_buf, "vFile:unlink:", 13) == 0)
     handle_unlink (own_buf);
+  else if (strncmp (own_buf, "vFile:readlink:", 15) == 0)
+    handle_readlink (own_buf, new_packet_len);
   else
     return 0;
 
Index: gdb-head/gdb/inf-child.c
===================================================================
--- gdb-head.orig/gdb/inf-child.c	2012-01-19 10:39:32.000000000 +0100
+++ gdb-head/gdb/inf-child.c	2012-01-19 10:40:27.000000000 +0100
@@ -29,6 +29,9 @@
 #include "inf-child.h"
 #include "gdb/fileio.h"
 
+#ifdef HAVE_SYS_PARAM_H
+#include <sys/param.h>		/* for MAXPATHLEN */
+#endif
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
@@ -299,6 +302,36 @@ inf_child_fileio_unlink (const char *fil
   return ret;
 }
 
+/* Read value of symbolic link FILENAME on the target.  Return a
+   null-terminated string allocated via xmalloc, or NULL if an error
+   occurs (and set *TARGET_ERRNO).  */
+static char *
+inf_child_fileio_readlink (const char *filename, int *target_errno)
+{
+  /* We support readlink only on systems that also provide a compile-time
+     maximum path length (MAXPATHLEN), at least for now.  */
+#if defined (HAVE_READLINK) && defined (MAXPATHLEN)
+  char buf[MAXPATHLEN];
+  int len;
+  char *ret;
+
+  len = readlink (filename, buf, sizeof buf);
+  if (len < 0)
+    {
+      *target_errno = inf_child_errno_to_fileio_error (errno);
+      return NULL;
+    }
+
+  ret = xmalloc (len + 1);
+  memcpy (ret, buf, len);
+  ret[len] = '\0';
+  return ret;
+#else
+  *target_errno = FILEIO_ENOSYS;
+  return NULL;
+#endif
+}
+
 
 struct target_ops *
 inf_child_target (void)
@@ -336,6 +369,7 @@ inf_child_target (void)
   t->to_fileio_pread = inf_child_fileio_pread;
   t->to_fileio_close = inf_child_fileio_close;
   t->to_fileio_unlink = inf_child_fileio_unlink;
+  t->to_fileio_readlink = inf_child_fileio_readlink;
   t->to_magic = OPS_MAGIC;
   return t;
 }
Index: gdb-head/gdb/remote.c
===================================================================
--- gdb-head.orig/gdb/remote.c	2012-01-19 10:39:32.000000000 +0100
+++ gdb-head/gdb/remote.c	2012-01-19 10:40:27.000000000 +0100
@@ -1238,6 +1238,7 @@ enum {
   PACKET_vFile_pwrite,
   PACKET_vFile_close,
   PACKET_vFile_unlink,
+  PACKET_vFile_readlink,
   PACKET_qXfer_auxv,
   PACKET_qXfer_features,
   PACKET_qXfer_libraries,
@@ -9358,6 +9359,44 @@ remote_hostio_unlink (const char *filena
 				     remote_errno, NULL, NULL);
 }
 
+/* Read value of symbolic link FILENAME on the remote target.  Return
+   a null-terminated string allocated via xmalloc, or NULL if an error
+   occurs (and set *REMOTE_ERRNO).  */
+
+static char *
+remote_hostio_readlink (const char *filename, int *remote_errno)
+{
+  struct remote_state *rs = get_remote_state ();
+  char *p = rs->buf;
+  char *attachment;
+  int left = get_remote_packet_size ();
+  int len, attachment_len;
+  int read_len;
+  char *ret;
+
+  remote_buffer_add_string (&p, &left, "vFile:readlink:");
+
+  remote_buffer_add_bytes (&p, &left, (const gdb_byte *) filename,
+			   strlen (filename));
+
+  len = remote_hostio_send_command (p - rs->buf, PACKET_vFile_readlink,
+				    remote_errno, &attachment,
+				    &attachment_len);
+
+  if (len < 0)
+    return NULL;
+
+  ret = xmalloc (len + 1);
+
+  read_len = remote_unescape_input (attachment, attachment_len,
+				    ret, len);
+  if (read_len != len)
+    error (_("Readlink returned %d, but %d bytes."), len, read_len);
+
+  ret[len] = '\0';
+  return ret;
+}
+
 static int
 remote_fileio_errno_to_host (int errnum)
 {
@@ -10679,6 +10718,7 @@ Specify the serial device it is connecte
   remote_ops.to_fileio_pread = remote_hostio_pread;
   remote_ops.to_fileio_close = remote_hostio_close;
   remote_ops.to_fileio_unlink = remote_hostio_unlink;
+  remote_ops.to_fileio_readlink = remote_hostio_readlink;
   remote_ops.to_supports_enable_disable_tracepoint = remote_supports_enable_disable_tracepoint;
   remote_ops.to_supports_string_tracing = remote_supports_string_tracing;
   remote_ops.to_trace_init = remote_trace_init;
@@ -11177,6 +11217,9 @@ Show the maximum size of the address (in
   add_packet_config_cmd (&remote_protocol_packets[PACKET_vFile_unlink],
 			 "vFile:unlink", "hostio-unlink", 0);
 
+  add_packet_config_cmd (&remote_protocol_packets[PACKET_vFile_readlink],
+			 "vFile:readlink", "hostio-readlink", 0);
+
   add_packet_config_cmd (&remote_protocol_packets[PACKET_vAttach],
 			 "vAttach", "attach", 0);
 
Index: gdb-head/gdb/target.c
===================================================================
--- gdb-head.orig/gdb/target.c	2012-01-19 10:39:32.000000000 +0100
+++ gdb-head/gdb/target.c	2012-01-19 10:40:27.000000000 +0100
@@ -3319,6 +3319,33 @@ target_fileio_unlink (const char *filena
   return -1;
 }
 
+/* Read value of symbolic link FILENAME on the target.  Return a
+   null-terminated string allocated via xmalloc, or NULL if an error
+   occurs (and set *TARGET_ERRNO).  */
+char *
+target_fileio_readlink (const char *filename, int *target_errno)
+{
+  struct target_ops *t;
+
+  for (t = default_fileio_target (); t != NULL; t = t->beneath)
+    {
+      if (t->to_fileio_readlink != NULL)
+	{
+	  char *ret = t->to_fileio_readlink (filename, target_errno);
+
+	  if (targetdebug)
+	    fprintf_unfiltered (gdb_stdlog,
+				"target_fileio_readlink (%s) = %s (%d)\n",
+				filename, ret? ret : "(nil)",
+				ret? 0 : *target_errno);
+	  return ret;
+	}
+    }
+
+  *target_errno = FILEIO_ENOSYS;
+  return NULL;
+}
+
 static void
 target_fileio_close_cleanup (void *opaque)
 {
Index: gdb-head/gdb/target.h
===================================================================
--- gdb-head.orig/gdb/target.h	2012-01-19 10:39:32.000000000 +0100
+++ gdb-head/gdb/target.h	2012-01-19 10:40:27.000000000 +0100
@@ -709,6 +709,11 @@ struct target_ops
        occurs (and set *TARGET_ERRNO).  */
     int (*to_fileio_unlink) (const char *filename, int *target_errno);
 
+    /* Read value of symbolic link FILENAME on the target.  Return a
+       null-terminated string allocated via xmalloc, or NULL if an error
+       occurs (and set *TARGET_ERRNO).  */
+    char *(*to_fileio_readlink) (const char *filename, int *target_errno);
+
 
     /* Tracepoint-related operations.  */
 
@@ -1546,6 +1551,11 @@ extern int target_fileio_close (int fd, 
    occurs (and set *TARGET_ERRNO).  */
 extern int target_fileio_unlink (const char *filename, int *target_errno);
 
+/* Read value of symbolic link FILENAME on the target.  Return a
+   null-terminated string allocated via xmalloc, or NULL if an error
+   occurs (and set *TARGET_ERRNO).  */
+extern char *target_fileio_readlink (const char *filename, int *target_errno);
+
 /* Read target file FILENAME.  The return value will be -1 if the transfer
    fails or is not supported; 0 if the object is empty; or the length
    of the object otherwise.  If a positive value is returned, a
Index: gdb-head/gdb/doc/gdb.texinfo
===================================================================
--- gdb-head.orig/gdb/doc/gdb.texinfo	2012-01-19 10:38:32.000000000 +0100
+++ gdb-head/gdb/doc/gdb.texinfo	2012-01-19 10:40:27.000000000 +0100
@@ -17455,6 +17455,10 @@ are:
 @tab @code{vFile:unlink}
 @tab @code{remote delete}
 
+@item @code{hostio-readlink-packet}
+@tab @code{vFile:readlink}
+@tab Host I/O
+
 @item @code{noack-packet}
 @tab @code{QStartNoAckMode}
 @tab Packet acknowledgment
@@ -36205,6 +36209,16 @@ error occurred.
 Delete the file at @var{pathname} on the target.  Return 0,
 or -1 if an error occurs.  @var{pathname} is a string.
 
+@item vFile:readlink: @var{filename}
+Read value of symbolic link @var{filename} on the target.  Return
+the number of bytes read, or -1 if an error occurs.
+
+The data read should be returned as a binary attachment on success.
+If zero bytes were read, the response should include an empty binary
+attachment (i.e.@: a trailing semicolon).  The return value is the
+number of target bytes read; the binary attachment may be longer if
+some characters were escaped.
+
 @end table
 
 @node Interrupts
Index: gdb-head/gdb/config.in
===================================================================
--- gdb-head.orig/gdb/config.in	2012-01-19 10:39:32.000000000 +0100
+++ gdb-head/gdb/config.in	2012-01-19 10:40:27.000000000 +0100
@@ -474,6 +474,9 @@
 /* Define to 1 if wcwidth is declared even after undefining macros. */
 #undef HAVE_RAW_DECL_WCWIDTH
 
+/* Define to 1 if you have the `readlink' function. */
+#undef HAVE_READLINK
+
 /* Define to 1 if you have the `realpath' function. */
 #undef HAVE_REALPATH
 
Index: gdb-head/gdb/configure
===================================================================
--- gdb-head.orig/gdb/configure	2012-01-19 10:40:05.000000000 +0100
+++ gdb-head/gdb/configure	2012-01-19 10:40:37.000000000 +0100
@@ -12932,7 +12932,7 @@ $as_echo "#define HAVE_WORKING_FORK 1" >
 fi
 
 for ac_func in canonicalize_file_name realpath getrusage getuid getgid \
-		pipe poll pread pread64 pwrite resize_term \
+		pipe poll pread pread64 pwrite readlink resize_term \
 		sbrk setpgid setpgrp setsid \
 		sigaction sigprocmask sigsetmask socketpair syscall \
 		ttrace wborder wresize setlocale iconvlist libiconvlist btowc \
Index: gdb-head/gdb/configure.ac
===================================================================
--- gdb-head.orig/gdb/configure.ac	2012-01-19 10:39:32.000000000 +0100
+++ gdb-head/gdb/configure.ac	2012-01-19 10:40:27.000000000 +0100
@@ -1064,7 +1064,7 @@ AC_FUNC_ALLOCA
 AC_FUNC_MMAP
 AC_FUNC_VFORK
 AC_CHECK_FUNCS([canonicalize_file_name realpath getrusage getuid getgid \
-		pipe poll pread pread64 pwrite resize_term \
+		pipe poll pread pread64 pwrite readlink resize_term \
 		sbrk setpgid setpgrp setsid \
 		sigaction sigprocmask sigsetmask socketpair syscall \
 		ttrace wborder wresize setlocale iconvlist libiconvlist btowc \
-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com