[PATCH v3 1/2] libxl: replace deprecated readdir_r() with readdir()

* [PATCH v3 1/2] libxl: replace deprecated readdir_r() with readdir()
@ 2016-06-03 16:50 Chris Patterson
  2016-06-03 16:50 ` [PATCH v3 2/2] libfsimage: " Chris Patterson
                   ` (2 more replies)
  0 siblings, 3 replies; 6+ messages in thread
From: Chris Patterson @ 2016-06-03 16:50 UTC (permalink / raw)
  To: xen-devel; +Cc: ian.jackson, Chris Patterson, wei.liu2

From: Chris Patterson <pattersonc@ainfosec.com>

Replace the usage of readdir_r() with readdir() to address a
compilation error under glibc due to the deprecation of readdir_r
for their next release (2.24) [1, 2].

Remove code specific to usage of readdir_r which is no longer required,
such as zalloc_dirent().

--

From the GNU libc manual [3]:
"
 It is expected that future versions of POSIX will obsolete readdir_r and
 mandate the level of thread safety for readdir which is provided by the
 GNU C Library and other implementations today.
"

There is a filed bug in the Austin Group Defect Tracker [4]  in which 'dalias'
proposes (in comment 0001632) that:
"
   I would like to propose an alternate solution. For readdir, replace the text:
    "The readdir() function need not be thread-safe."
   with:
    "If multiple threads call the readdir() function with the same directory
    stream argument and without synchronization to preclude simultaneous
    access, then the behavior is undefined."

   With this change, the clunky readdir_r function is no longer needed or
   useful, and should probably be deprecated. As the only reasonable way
   to meet the implementation requirements for readdir is to have the dirent
   buffer in the DIR structure, this change should not require any change to
   existing implementations.
"

[1] https://sourceware.org/ml/libc-alpha/2016-02/msg00093.html
[2] https://sourceware.org/bugzilla/show_bug.cgi?id=19056
[3] https://www.gnu.org/software/libc/manual/html_node/Reading_002fClosing-Directory.html
[4] http://austingroupbugs.net/view.php?id=696

Signed-off-by: Chris Patterson <pattersonc@ainfosec.com>
---

v2:
- Additional detail in commit message
- Fix readdir loop logic (do not treat NULL as error)
- Cleanup additional (no longer used) code

v3:
- Restore original loop & error handling

 tools/libxl/libxl_pvusb.c | 24 ++++++------------------
 tools/libxl/libxl_utils.c |  8 +++-----
 2 files changed, 9 insertions(+), 23 deletions(-)

diff --git a/tools/libxl/libxl_pvusb.c b/tools/libxl/libxl_pvusb.c
index 9f1e842..ec97ff8 100644
--- a/tools/libxl/libxl_pvusb.c
+++ b/tools/libxl/libxl_pvusb.c
@@ -508,19 +508,10 @@ int libxl_devid_to_device_usbctrl(libxl_ctx *ctx,
     return rc;
 }
 
-static void *zalloc_dirent(libxl__gc *gc, const char *dirpath)
-{
-    size_t need = offsetof(struct dirent, d_name) +
-                  pathconf(dirpath, _PC_NAME_MAX) + 1;
-
-    return libxl__zalloc(gc, need);
-}
-
 static char *usbdev_busaddr_to_busid(libxl__gc *gc, int bus, int addr)
 {
     DIR *dir;
     char *busid = NULL;
-    struct dirent *de_buf;
     struct dirent *de;
 
     /* invalid hostbus or hostaddr */
@@ -533,16 +524,15 @@ static char *usbdev_busaddr_to_busid(libxl__gc *gc, int bus, int addr)
         return NULL;
     }
 
-    de_buf = zalloc_dirent(gc, SYSFS_USB_DEV);
-
     for (;;) {
         char *filename;
         void *buf;
         int busnum = -1;
         int devnum = -1;
 
-        int r = readdir_r(dir, de_buf, &de);
-        if (r) {
+        errno = 0;
+        de = readdir(dir);
+        if (!de && errno) {
             LOGE(ERROR, "failed to readdir %s", SYSFS_USB_DEV);
             break;
         }
@@ -1157,7 +1147,6 @@ static int usbdev_get_all_interfaces(libxl__gc *gc, const char *busid,
 {
     DIR *dir;
     char *buf;
-    struct dirent *de_buf;
     struct dirent *de;
     int rc;
 
@@ -1172,12 +1161,11 @@ static int usbdev_get_all_interfaces(libxl__gc *gc, const char *busid,
         return ERROR_FAIL;
     }
 
-    de_buf = zalloc_dirent(gc, SYSFS_USB_DEV);
-
     for (;;) {
-        int r = readdir_r(dir, de_buf, &de);
+        errno = 0;
+        de = readdir(dir);
 
-        if (r) {
+        if (!de && errno) {
             LOGE(ERROR, "failed to readdir %s", SYSFS_USB_DEV);
             rc = ERROR_FAIL;
             goto out;
diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
index ceb8825..4ca6bcb 100644
--- a/tools/libxl/libxl_utils.c
+++ b/tools/libxl/libxl_utils.c
@@ -548,14 +548,12 @@ int libxl__remove_directory(libxl__gc *gc, const char *dirpath)
         goto out;
     }
 
-    size_t need = offsetof(struct dirent, d_name) +
-        pathconf(dirpath, _PC_NAME_MAX) + 1;
-    struct dirent *de_buf = libxl__zalloc(gc, need);
     struct dirent *de;
 
     for (;;) {
-        int r = readdir_r(d, de_buf, &de);
-        if (r) {
+        errno = 0;
+        de = readdir(d);
+        if (!de && errno) {
             LOGE(ERROR, "failed to readdir %s for removal", dirpath);
             rc = ERROR_FAIL;
             break;
-- 
2.1.4


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