RFC: procfs file descriptor leak patch

[Tom Tromey <tromey at redhat dot com>]

Here's the final file descriptor leak patch.

This one only touches procfs.c.  

This does the usual cleanup transform, but it also corrects a number
of erroneous assumptions about the result of calls to open.  In
particular, the result can be 0 on success.  Of course, that would be
extremely weird in gdb, probably impossible -- but code like this is
confusing even if it can't be triggered.  Also, there is one case
where the result of open is compared "== 0" and apparently this is
taken to mean an error occurred.  This also fixes a potential memory
leak in load_syscalls.

I am sending this for completeness' sake.  I don't have whatever
machines this patch might apply to.  I just noticed these oddities
when reading the code, and thought I would point them out in patch
form.

Tom

2008-10-28  Tom Tromey  <tromey@redhat.com>

	* procfs.c (load_syscalls): Make a cleanup.
	(open_procinfo_files): fd==0 is ok.

diff --git a/gdb/procfs.c b/gdb/procfs.c
index 248dd3a..d7b823f 100644
--- a/gdb/procfs.c
+++ b/gdb/procfs.c
@@ -627,7 +627,7 @@ open_procinfo_files (procinfo *pi, int which)
     else
       strcat (tmp, "/ctl");
     fd = open_with_retry (tmp, O_WRONLY);
-    if (fd <= 0)
+    if (fd < 0)
       return 0;		/* fail */
     pi->ctl_fd = fd;
     break;
@@ -636,7 +636,7 @@ open_procinfo_files (procinfo *pi, int which)
       return 0;		/* there is no 'as' file descriptor for an lwp */
     strcat (tmp, "/as");
     fd = open_with_retry (tmp, O_RDWR);
-    if (fd <= 0)
+    if (fd < 0)
       return 0;		/* fail */
     pi->as_fd = fd;
     break;
@@ -646,7 +646,7 @@ open_procinfo_files (procinfo *pi, int which)
     else
       strcat (tmp, "/status");
     fd = open_with_retry (tmp, O_RDONLY);
-    if (fd <= 0)
+    if (fd < 0)
       return 0;		/* fail */
     pi->status_fd = fd;
     break;
@@ -670,13 +670,13 @@ open_procinfo_files (procinfo *pi, int which)
 
 #ifdef PIOCTSTATUS	/* OSF */
   /* Only one FD; just open it. */
-  if ((fd = open_with_retry (pi->pathname, O_RDWR)) == 0)
+  if ((fd = open_with_retry (pi->pathname, O_RDWR)) < 0)
     return 0;
 #else			/* Sol 2.5, Irix, other? */
   if (pi->tid == 0)	/* Master procinfo for the process */
     {
       fd = open_with_retry (pi->pathname, O_RDWR);
-      if (fd <= 0)
+      if (fd < 0)
 	return 0;	/* fail */
     }
   else			/* LWP thread procinfo */
@@ -690,7 +690,7 @@ open_procinfo_files (procinfo *pi, int which)
 	return 0;	/* fail */
 
       /* Now obtain the file descriptor for the LWP. */
-      if ((fd = ioctl (process->ctl_fd, PIOCOPENLWP, &lwpid)) <= 0)
+      if ((fd = ioctl (process->ctl_fd, PIOCOPENLWP, &lwpid)) < 0)
 	return 0;	/* fail */
 #else			/* Irix, other? */
       return 0;		/* Don't know how to open threads */
@@ -926,6 +926,7 @@ load_syscalls (procinfo *pi)
   prsysent_t header;
   prsyscall_t *syscalls;
   int i, size, maxcall;
+  struct cleanup *cleanups;
 
   pi->num_syscalls = 0;
   pi->syscall_names = 0;
@@ -937,6 +938,7 @@ load_syscalls (procinfo *pi)
     {
       error (_("load_syscalls: Can't open /proc/%d/sysent"), pi->pid);
     }
+  cleanups = make_cleanup_close (sysent_fd);
 
   size = sizeof header - sizeof (prsyscall_t);
   if (read (sysent_fd, &header, size) != size)
@@ -951,12 +953,10 @@ load_syscalls (procinfo *pi)
 
   size = header.pr_nsyscalls * sizeof (prsyscall_t);
   syscalls = xmalloc (size);
+  make_cleanup (free_current_contents, &syscalls);
 
   if (read (sysent_fd, syscalls, size) != size)
-    {
-      xfree (syscalls);
-      error (_("load_syscalls: Error reading /proc/%d/sysent"), pi->pid);
-    }
+    error (_("load_syscalls: Error reading /proc/%d/sysent"), pi->pid);
 
   /* Find maximum syscall number.  This may not be the same as
      pr_nsyscalls since that value refers to the number of entries
@@ -1010,8 +1010,7 @@ load_syscalls (procinfo *pi)
       pi->syscall_names[callnum][size-1] = '\0';
     }
 
-  close (sysent_fd);
-  xfree (syscalls);
+  do_cleanups (cleanups);
 }
 
 /* Function: free_syscalls