[PATCH v1 5/6] gdb/linux-tdep: migrate linux_find_memory_regions_full to file_reader_t

The previous implementation of linux_find_memory_regions_full could
still return success even when none of the /proc/PID/[s]maps files
existed, or all reads returned 0 bytes (this last case can happen on
Linux when the thread-group leader has exited).
As a result, the function could incorrectly succeed, allowing core
dump generation via the gcore command.
This logical defect was allowing, by chance, the function to return
success and hence, allowing fortuitously the coredump generation via
gcore command (see gcore-stale-thread test for more details).

A previous patch in this patch series fixed this issue by using the
first LWP ID of the current inferior instead of relying on the PID.
This patch adapts the code to use file_reader_t and makes the function
return an error if reading any of the procfs files fails.
---
 gdb/linux-tdep.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index a8dab0d6d5e..628f73969d3 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -1829,25 +1829,22 @@ linux_find_memory_regions_full (struct gdbarch *gdbarch,
 	}
     }
 
-  std::string maps_filename = string_printf ("/proc/%ld/smaps", ptid.lwp ());
-
-  gdb::unique_xmalloc_ptr<char> data
-    = target_fileio_read_stralloc (NULL, maps_filename.c_str ());
+  std::vector<struct smaps_data> smaps;
 
-  if (data == NULL)
+  file_reader_t<char> smaps_freader
+    (string_printf ("/proc/%ld/smaps", ptid.lwp ()));
+  if (smaps_freader)
+    smaps = parse_smaps_data (smaps_freader);
+  else
     {
       /* Older Linux kernels did not support /proc/PID/smaps.  */
-      maps_filename = string_printf ("/proc/%ld/maps", ptid.lwp ());
-      data = target_fileio_read_stralloc (NULL, maps_filename.c_str ());
-
-      if (data == nullptr)
+      file_reader_t<char> maps_freader
+	(string_printf ("/proc/%ld/maps", ptid.lwp ()));
+      if (!maps_freader)
 	return false;
+      smaps = parse_smaps_data (maps_freader);
     }
 
-  /* Parse the contents of smaps into a vector.  */
-  std::vector<struct smaps_data> smaps
-    = parse_smaps_data (data.get (), maps_filename);
-
   for (const struct smaps_data &map : smaps)
     {
       /* Invoke the callback function to create the corefile segment.  */
-- 
2.55.0