[rfc v2][4/6] Readlink as file I/O target operation

[rfc v2][4/6] Readlink as file I/O target operation

[Ulrich Weigand]

Hello,

this adds another operation: target_fileio_readlink.  This is needed to
access those /proc files where the important information is actually in
the link text, e.g. /proc/.../exe or /proc/.../cwd.

This requires a new vFile:readlink packet type.

Note that readlink may not be supported on some native systems, in which
case the target_fileio_readlink call fails with an error.

Bye,
Ulrich


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	2012-01-13 18:44:34.000000000 +0100
+++ gdb-head/gdb/gdbserver/hostio.c	2012-01-13 18:45:57.000000000 +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	2012-01-13 18:45:57.000000000 +0100
+++ gdb-head/gdb/inf-child.c	2012-01-13 18:45:57.000000000 +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 remote target.  Return
+   a null-terminated string allocated via xmalloc, or NULL if an error
+   occurs (and set *REMOTE_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_EUNKNOWN;
+  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	2012-01-13 18:45:57.000000000 +0100
+++ gdb-head/gdb/remote.c	2012-01-13 18:45:57.000000000 +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	2012-01-13 18:45:57.000000000 +0100
+++ gdb-head/gdb/target.c	2012-01-13 18:45:57.000000000 +0100
@@ -3308,6 +3308,33 @@ target_fileio_unlink (const char *filena
   return -1;
 }
 
+/* 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).  */
+char *
+target_fileio_readlink (const char *filename, int *target_errno)
+{
+  struct target_ops *t;
+
+  for (t = current_target.beneath; 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_EUNKNOWN;
+  return NULL;
+}
+
 static void
 target_fileio_close_cleanup (void *opaque)
 {
Index: gdb-head/gdb/target.h
===================================================================
--- gdb-head.orig/gdb/target.h	2012-01-13 18:45:57.000000000 +0100
+++ gdb-head/gdb/target.h	2012-01-13 18:45:57.000000000 +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 remote target.  Return
+       a null-terminated string allocated via xmalloc, or NULL if an error
+       occurs (and set *REMOTE_ERRNO).  */
+    char *(*to_fileio_readlink) (const char *filename, int *remote_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 remote target.  Return
+   a null-terminated string allocated via xmalloc, or NULL if an error
+   occurs (and set *REMOTE_ERRNO).  */
+extern char *target_fileio_readlink (const char *filename, int *remote_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	2012-01-13 18:44:34.000000000 +0100
+++ gdb-head/gdb/doc/gdb.texinfo	2012-01-13 18:45:57.000000000 +0100
@@ -17450,6 +17450,10 @@ 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
@@ -36193,6 +36197,16 @@ 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{pathname}
+Read value of symbolic link @var{pathname} 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	2012-01-13 18:45:57.000000000 +0100
+++ gdb-head/gdb/config.in	2012-01-13 18:45:57.000000000 +0100
@@ -468,6 +468,9 @@
 /* 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	2012-01-13 18:45:57.000000000 +0100
+++ gdb-head/gdb/configure	2012-01-13 18:45:57.000000000 +0100
@@ -12915,7 +12915,7 @@ $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	2012-01-13 18:45:57.000000000 +0100
+++ gdb-head/gdb/configure.ac	2012-01-13 18:45:57.000000000 +0100
@@ -1056,7 +1056,7 @@ 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

Re: [rfc v2][4/6] Readlink as file I/O target operation

[Eli Zaretskii]

> Date: Fri, 13 Jan 2012 19:15:12 +0100 (CET)
> From: "Ulrich Weigand" <uweigand@de.ibm.com>
> 
> --- gdb-head.orig/gdb/doc/gdb.texinfo	2012-01-13 18:44:34.000000000 +0100
> +++ gdb-head/gdb/doc/gdb.texinfo	2012-01-13 18:45:57.000000000 +0100
> @@ -17450,6 +17450,10 @@ 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
> @@ -36193,6 +36197,16 @@ 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{pathname}
> +Read value of symbolic link @var{pathname} 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.
> +

This part is okay, but please don't use "pathname" when you really
mean "file name".  GNU Coding Standards frown on using "path" or its
derivatives for anything but PATH-style directory lists.

Thanks.

Re: [rfc v2][4/6] Readlink as file I/O target operation

[Ulrich Weigand]

Eli Zaretskii wrote:
> > Date: Fri, 13 Jan 2012 19:15:12 +0100 (CET)
> > From: "Ulrich Weigand" <uweigand@de.ibm.com>
> > @@ -36193,6 +36197,16 @@ 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{pathname}
> > +Read value of symbolic link @var{pathname} on the target.  Return
> > +the number of bytes read, or -1 if an error occurs.
> 
> This part is okay, but please don't use "pathname" when you really
> mean "file name".  GNU Coding Standards frown on using "path" or its
> derivatives for anything but PATH-style directory lists.

I'll be happy to use "filename" instead, but the currently existing
packets (open, unlink) also use "pathname" today.  Should those be
changed to "filename" too?

(B.t.w. note that those packets are directly related to the corresponding
POSIX routines open/unlink/readlink -- the documentation of those routines,
whether in POSIX itself or in the corresponding Linux man pages consistently
refers to those arguments as "path" or "pathname" ...  I'm wondering whether
it is a deliberate decision on the part of the GNU Coding Standards to deviate
from established terminology in that area?)

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com

Re: [rfc v2][4/6] Readlink as file I/O target operation

[Eli Zaretskii]

> Date: Mon, 16 Jan 2012 13:32:23 +0100 (CET)
> From: "Ulrich Weigand" <uweigand@de.ibm.com>
> Cc: gdb-patches@sourceware.org
> 
> > > +@item vFile:readlink: @var{pathname}
> > > +Read value of symbolic link @var{pathname} on the target.  Return
> > > +the number of bytes read, or -1 if an error occurs.
> > 
> > This part is okay, but please don't use "pathname" when you really
> > mean "file name".  GNU Coding Standards frown on using "path" or its
> > derivatives for anything but PATH-style directory lists.
> 
> I'll be happy to use "filename" instead, but the currently existing
> packets (open, unlink) also use "pathname" today.  Should those be
> changed to "filename" too?

In general, yes.  But I cannot in good faith ask you to do that as
part of this patch.  So let's make a first small step in this
1000-mile journey by using "filename" in just this part.  I'll add to
my todo to fix the rest, if no one beats me to it.

Thanks.

> (B.t.w. note that those packets are directly related to the corresponding
> POSIX routines open/unlink/readlink -- the documentation of those routines,
> whether in POSIX itself or in the corresponding Linux man pages consistently
> refers to those arguments as "path" or "pathname" ...  I'm wondering whether
> it is a deliberate decision on the part of the GNU Coding Standards to deviate
> from established terminology in that area?)

Everyone else calls the system "Linux", while the FSF insists on
"GNU/Linux".  Nothing new here.

Re: [rfc v2][4/6] Readlink as file I/O target operation

[Ulrich Weigand]

Eli Zaretskii wrote:
> > Date: Mon, 16 Jan 2012 13:32:23 +0100 (CET)
> > From: "Ulrich Weigand" <uweigand@de.ibm.com>
> > Cc: gdb-patches@sourceware.org
> > I'll be happy to use "filename" instead, but the currently existing
> > packets (open, unlink) also use "pathname" today.  Should those be
> > changed to "filename" too?
> 
> In general, yes.  But I cannot in good faith ask you to do that as
> part of this patch.  So let's make a first small step in this
> 1000-mile journey by using "filename" in just this part.  I'll add to
> my todo to fix the rest, if no one beats me to it.

Fair enough.  Appended below is the updated doc part of the patch,
just making the pathname -> filename change for readlink.

Thanks,
Ulrich


Index: gdb-head/gdb/doc/gdb.texinfo
===================================================================
--- gdb-head.orig/gdb/doc/gdb.texinfo	2012-01-13 18:44:34.000000000 +0100
+++ gdb-head/gdb/doc/gdb.texinfo	2012-01-16 15:03:17.000000000 +0100
@@ -17450,6 +17450,10 @@ 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
@@ -36193,6 +36197,16 @@ 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

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com

Re: [rfc v2][4/6] Readlink as file I/O target operation

[Pedro Alves]

Hi,

On 01/13/2012 06:15 PM, Ulrich Weigand wrote:
> +/* 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 *
> +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_EUNKNOWN;

Should this be FILEIO_ENOSYS ?

-- 
Pedro Alves

Re: [rfc v2][4/6] Readlink as file I/O target operation

[Eli Zaretskii]

> Date: Mon, 16 Jan 2012 15:07:43 +0100 (CET)
> From: "Ulrich Weigand" <uweigand@de.ibm.com>
> Cc: gdb-patches@sourceware.org
> 
> Eli Zaretskii wrote:
> > > Date: Mon, 16 Jan 2012 13:32:23 +0100 (CET)
> > > From: "Ulrich Weigand" <uweigand@de.ibm.com>
> > > Cc: gdb-patches@sourceware.org
> > > I'll be happy to use "filename" instead, but the currently existing
> > > packets (open, unlink) also use "pathname" today.  Should those be
> > > changed to "filename" too?
> > 
> > In general, yes.  But I cannot in good faith ask you to do that as
> > part of this patch.  So let's make a first small step in this
> > 1000-mile journey by using "filename" in just this part.  I'll add to
> > my todo to fix the rest, if no one beats me to it.
> 
> Fair enough.  Appended below is the updated doc part of the patch,
> just making the pathname -> filename change for readlink.

Fine with me, thanks.

Re: [rfc v2][4/6] Readlink as file I/O target operation

[Ulrich Weigand]

Pedro Alves wrote:
> On 01/13/2012 06:15 PM, Ulrich Weigand wrote:
> > +  *target_errno = FILEIO_EUNKNOWN;
> 
> Should this be FILEIO_ENOSYS ?

Makes sense.   I guess the same then needs to be returned
from the various target_ routines if the operation is not
supported on the current target.

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com