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

Ulrich Weigand
2012-01-13T18:15:38Z

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 \