Return target_xfer_status in to_xfer_partial

This patch does the conversion of to_xfer_partial from

    LONGEST (*to_xfer_partial) (struct target_ops *ops,
				enum target_object object, const char *annex,
				gdb_byte *readbuf, const gdb_byte *writebuf,
				ULONGEST offset, ULONGEST len);

to

    enum target_xfer_status (*to_xfer_partial) (struct target_ops *ops,
				enum target_object object, const char *annex,
				gdb_byte *readbuf, const gdb_byte *writebuf,
				ULONGEST offset, ULONGEST len, ULONGEST *xfered_len);

It changes to_xfer_partial return the transfer status and the transfered
length by *XFERED_LEN.  Generally, the return status has three stats,

 - TARGET_XFER_OK,
 - TARGET_XFER_EOF,
 - TARGET_XFER_E_XXXX,

See the comments to them in 'enum target_xfer_status'.  Note that
Pedro suggested not name TARGET_XFER_DONE, as it is confusing,
compared with "TARGET_XFER_OK".  We finally name it TARGET_XFER_EOF.

With this change, GDB core can handle unavailable data in a convenient
way.

The rationale behind this change was mentioned here
https://sourceware.org/ml/gdb-patches/2013-10/msg00761.html

Consider an object/value like this:

  0          100      150        200           512
  DDDDDDDDDDDxxxxxxxxxDDDDDD...DDIIIIIIIIIIII..III

where D is valid data, and xxx is unavailable data, and I is beyond
the end of the object (Invalid).  Currently, if we start the
xfer at 0, requesting, say 512 bytes, we'll first get back 100 bytes.
The xfer machinery then retries fetching [100,512), and gets back
TARGET_XFER_E_UNAVAILABLE.  That's sufficient when you're either
interested in either having the whole of the 512 bytes available,
or erroring out.  But, in this scenario, we're interested in
the data at [150,512).  The problem is that the last
TARGET_XFER_E_UNAVAILABLE gives us no indication where to
start the read next.  We'd need something like:

get me [0,512) >>>
     <<< here's [0,100), *xfered_len is 100, returns TARGET_XFER_OK

get me [100,512)  >>> (**1)
     <<< [100,150) is unavailable, *xfered_len is 50, return TARGET_XFER_E_UNAVAILABLE.

get me [150,512) >>>
     <<< here's [150,200), *xfered_len is 50, return TARGET_XFER_OK.

get me [200,512) >>>
     <<< no more data, return TARGET_XFER_EOF.

This naturally implies pushing down the decision of whether
to return TARGET_XFER_E_UNAVAILABLE or something else
down to the target.  (Which kinds of leads back to tfile
itself reading from RO memory from file (though we could
export a function in exec.c for that that tfile delegates to,
instead of re-adding the old code).

Beside this change, we also add a macro TARGET_XFER_STATUS_ERROR_P to
check whether a status is an error or not, to stop using "status < 0".
This patch also eliminates the comparison between status and 0.

No target implementations to to_xfer_partial adapts this new
interface.  The interface still behaves as before.

gdb:

2014-02-11  Yao Qi  <yao@codesourcery.com>

	* target.h (enum target_xfer_error): Rename to ...
	(enum target_xfer_status): ... it.  New.  All users updated.
	(enum target_xfer_status) <TARGET_XFER_OK>, <TARGET_XFER_EOF>:
	New.
	(TARGET_XFER_STATUS_ERROR_P): New macro.
	(target_xfer_error_to_string): Remove declaration.
	(target_xfer_status_to_string): Declare.
	(target_xfer_partial_ftype): Adjust it.
	(struct target_ops) <to_xfer_partial>: Return
	target_xfer_status.  Add argument xfered_len.  Update
	comments.
	* target.c (target_xfer_error_to_string): Rename to ...
	(target_xfer_status_to_string): ... it.  New.  All callers
	updated.
	(target_read_live_memory): Likewise.  Call target_xfer_partial
	instead of target_read.
	(memory_xfer_live_readonly_partial): Return
	target_xfer_status.  Add argument xfered_len.
	(raw_memory_xfer_partial): Likewise.
	(memory_xfer_partial_1): Likewise.
	(memory_xfer_partial): Likewise.
	(target_xfer_partial): Likewise.  Check *XFERED_LEN is set
	properly.  Update debug message.
	(default_xfer_partial, current_xfer_partial): Likewise.
	(target_write_partial): Likewise.
	(target_read_partial): Likewise.  All callers updated.
	(read_whatever_is_readable): Likewise.
	(target_write_with_progress): Likewise.
	(target_read_alloc_1): Likewise.

	* aix-thread.c (aix_thread_xfer_partial): Likewise.
	* auxv.c (procfs_xfer_auxv): Likewise.
	(ld_so_xfer_auxv, memory_xfer_auxv): Likewise.
	* bfd-target.c (target_bfd_xfer_partial): Likewise.
	* bsd-kvm.c (bsd_kvm_xfer_partial): Likewise.
	* bsd-uthread.c (bsd_uthread_xfer_partia): Likewise.
	* corefile.c (read_memory): Adjust.
	* corelow.c (core_xfer_partial): Likewise.
	* ctf.c (ctf_xfer_partial): Likewise.
	* darwin-nat.c (darwin_read_dyld_info): Likewise.  All callers
	updated.
	(darwin_xfer_partial): Likewise.
	* exec.c (section_table_xfer_memory_partial): Likewise.  All
	callers updated.
	(exec_xfer_partial): Likewise.
	* exec.h (section_table_xfer_memory_partial): Update
	declaration.
	* gnu-nat.c (gnu_xfer_memory): Likewise.  Assert 'res' is not
	negative.
	(gnu_xfer_partial): Likewise.
	* ia64-hpux-nat.c (ia64_hpux_xfer_memory_no_bs): Likewise.
	(ia64_hpux_xfer_memory, ia64_hpux_xfer_uregs): Likewise.
	(ia64_hpux_xfer_solib_got): Likewise.
	* inf-ptrace.c (inf_ptrace_xfer_partial): Likewise.  Change
	type of 'partial_len' to ULONGEST.
	* inf-ttrace.c (inf_ttrace_xfer_partial): Likewise.
	* linux-nat.c (linux_xfer_siginfo ): Likewise.
	(linux_nat_xfer_partial): Likewise.
	(linux_proc_xfer_partial, linux_xfer_partial): Likewise.
	(linux_proc_xfer_spu, linux_nat_xfer_osdata): Likewise.
	* monitor.c (monitor_xfer_memory): Likewise.
	(monitor_xfer_partial): Likewise.
	* procfs.c (procfs_xfer_partial): Likewise.
	* record-btrace.c (record_btrace_xfer_partial): Likewise.
	* record-full.c (record_full_xfer_partial): Likewise.
	(record_full_core_xfer_partial): Likewise.
	* remote-sim.c (gdbsim_xfer_memory): Likewise.
	(gdbsim_xfer_partial): Likewise.
	* remote.c (remote_write_bytes_aux): Likewise.  All callers
	updated.
	(remote_write_bytes, remote_read_bytes): Likewise.  All
	callers updated.
	(remote_flash_erase): Likewise.  All callers updated.
	(remote_write_qxfer): Likewise.  All callers updated.
	(remote_read_qxfer): Likewise.  All callers updated.
	(remote_xfer_partial): Likewise.
	* rs6000-nat.c (rs6000_xfer_partial): Likewise.
	(rs6000_xfer_shared_libraries): Likewise.
	* sol-thread.c (sol_thread_xfer_partial): Likewise.
	(sol_thread_xfer_partial): Likewise.
	* sparc-nat.c (sparc_xfer_wcookie): Likewise.
	(sparc_xfer_partial): Likewise.
	* spu-linux-nat.c (spu_proc_xfer_spu): Likewise.  All callers
	updated.
	(spu_xfer_partial): Likewise.
	* spu-multiarch.c (spu_xfer_partial): Likewise.
	* tracepoint.c (tfile_xfer_partial): Likewise.
	* windows-nat.c (windows_xfer_memory): Likewise.
	(windows_xfer_shared_libraries): Likewise.
	(windows_xfer_partial): Likewise.
	* valprint.c: Replace 'target_xfer_error' with
	'target_xfer_status' in comments.

1 files changed, 18 insertions, 11 deletions

diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
index dc3746b..edcad5a 100644
--- a/gdb/inf-ptrace.c
+++ b/gdb/inf-ptrace.c
@@ -459,11 +459,11 @@ inf_ptrace_wait (struct target_ops *ops,
    inferior's OBJECT:ANNEX space and GDB's READBUF/WRITEBUF buffer.
    Return the number of bytes actually transferred.  */
 
-static LONGEST
+static enum target_xfer_status
 inf_ptrace_xfer_partial (struct target_ops *ops, enum target_object object,
 			 const char *annex, gdb_byte *readbuf,
 			 const gdb_byte *writebuf,
-			 ULONGEST offset, ULONGEST len)
+			 ULONGEST offset, ULONGEST len, ULONGEST *xfered_len)
 {
   pid_t pid = ptid_get_pid (inferior_ptid);
 
@@ -490,13 +490,16 @@ inf_ptrace_xfer_partial (struct target_ops *ops, enum target_object object,
 
 	errno = 0;
 	if (ptrace (PT_IO, pid, (caddr_t)&piod, 0) == 0)
-	  /* Return the actual number of bytes read or written.  */
-	  return piod.piod_len;
+	  {
+	    *xfered_len = piod.piod_len;
+	    /* Return the actual number of bytes read or written.  */
+	    return TARGET_XFER_OK;
+	  }
 	/* If the PT_IO request is somehow not supported, fallback on
 	   using PT_WRITE_D/PT_READ_D.  Otherwise we will return zero
 	   to indicate failure.  */
 	if (errno != EINVAL)
-	  return 0;
+	  return TARGET_XFER_EOF;
       }
 #endif
       {
@@ -506,7 +509,7 @@ inf_ptrace_xfer_partial (struct target_ops *ops, enum target_object object,
 	  gdb_byte byte[sizeof (PTRACE_TYPE_RET)];
 	} buffer;
 	ULONGEST rounded_offset;
-	LONGEST partial_len;
+	ULONGEST partial_len;
 
 	/* Round the start offset down to the next long word
 	   boundary.  */
@@ -552,7 +555,7 @@ inf_ptrace_xfer_partial (struct target_ops *ops, enum target_object object,
 			(PTRACE_TYPE_ARG3)(uintptr_t)rounded_offset,
 			buffer.word);
 		if (errno)
-		  return 0;
+		  return TARGET_XFER_EOF;
 	      }
 	  }
 
@@ -563,13 +566,14 @@ inf_ptrace_xfer_partial (struct target_ops *ops, enum target_object object,
 				  (PTRACE_TYPE_ARG3)(uintptr_t)rounded_offset,
 				  0);
 	    if (errno)
-	      return 0;
+	      return TARGET_XFER_EOF;
 	    /* Copy appropriate bytes out of the buffer.  */
 	    memcpy (readbuf, buffer.byte + (offset - rounded_offset),
 		    partial_len);
 	  }
 
-	return partial_len;
+	*xfered_len = partial_len;
+	return TARGET_XFER_OK;
       }
 
     case TARGET_OBJECT_UNWIND_TABLE:
@@ -592,8 +596,11 @@ inf_ptrace_xfer_partial (struct target_ops *ops, enum target_object object,
 
 	errno = 0;
 	if (ptrace (PT_IO, pid, (caddr_t)&piod, 0) == 0)
-	  /* Return the actual number of bytes read or written.  */
-	  return piod.piod_len;
+	  {
+	    *xfered_len = piod.piod_len;
+	    /* Return the actual number of bytes read or written.  */
+	    return TARGET_XFER_OK;
+	  }
       }
 #endif
       return TARGET_XFER_E_IO;