[Xen-devel] [PATCH V8 2/7] libxl_read_file_contents: add new entry to read sysfs file

[Chunyan Liu <cyliu@xxxxxxxx>]

Sysfs file has size=4096 but actual file content is less than that.
Current libxl_read_file_contents will treat it as error when file size
and actual file content differs, so reading sysfs file content with
this function always fails.

Add a new entry libxl_read_sysfs_file_contents to handle sysfs file
specially. It would be used in later pvusb work.

Signed-off-by: Chunyan Liu <cyliu@xxxxxxxx>

---
Changes:
  - Update libxl_read_sysfs_file_contents to follow internal
    function definition rules, and adjust related implementation.

 tools/libxl/libxl_internal.h |  4 +++
 tools/libxl/libxl_utils.c    | 61 ++++++++++++++++++++++++++++++++++----------
 2 files changed, 51 insertions(+), 14 deletions(-)

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index ab981d2..a3a5cc1 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -4022,6 +4022,10 @@ void libxl__bitmap_copy_best_effort(libxl__gc *gc, 
libxl_bitmap *dptr,
 
 int libxl__count_physical_sockets(libxl__gc *gc, int *sockets);
 #endif
+_hidden int libxl__read_sysfs_file_contents(libxl__gc *gc,
+                                            const char *filename,
+                                            void **data_r,
+                                            int *datalen_r);
 
 /*
  * Local variables:
diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
index e42422a..9c5c4d0 100644
--- a/tools/libxl/libxl_utils.c
+++ b/tools/libxl/libxl_utils.c
@@ -322,9 +322,10 @@ out:
     return rc;
 }
 
-int libxl_read_file_contents(libxl_ctx *ctx, const char *filename,
-                             void **data_r, int *datalen_r) {
-    GC_INIT(ctx);
+static int read_file_contents_core(libxl__gc *gc, const char *filename,
+                                   void **data_r, int *datalen_r,
+                                   bool tolerate_shrinking_file)
+{
     FILE *f = 0;
     uint8_t *data = 0;
     int datalen = 0;
@@ -359,20 +360,35 @@ int libxl_read_file_contents(libxl_ctx *ctx, const char 
*filename,
     datalen = stab.st_size;
 
     if (stab.st_size && data_r) {
-        data = malloc(datalen);
+        data = malloc(datalen + 1);
         if (!data) goto xe;
 
-        rs = fread(data, 1, datalen, f);
-        if (rs != datalen) {
-            if (ferror(f))
+        rs = fread(data, 1, datalen + 1, f);
+        if (rs > datalen) {
+            LOG(ERROR, "%s increased size while we were reading it",
+                filename);
+            goto xe;
+        }
+
+        if (rs < datalen) {
+            if (ferror(f)) {
                 LOGE(ERROR, "failed to read %s", filename);
-            else if (feof(f))
-                LOG(ERROR, "%s changed size while we were reading it",
-                   filename);
-            else
+                goto xe;
+            } else if (feof(f)) {
+                if (tolerate_shrinking_file) {
+                    datalen = rs;
+                } else {
+                    LOG(ERROR, "%s shrunk size while we were reading it",
+                        filename);
+                    goto xe;
+                }
+            } else {
                 abort();
-            goto xe;
+            }
         }
+
+        data = realloc(data, datalen);
+        if (!data) goto xe;
     }
 
     if (fclose(f)) {
@@ -384,11 +400,9 @@ int libxl_read_file_contents(libxl_ctx *ctx, const char 
*filename,
     if (data_r) *data_r = data;
     if (datalen_r) *datalen_r = datalen;
 
-    GC_FREE;
     return 0;
 
  xe:
-    GC_FREE;
     e = errno;
     assert(e != ENOENT);
     if (f) fclose(f);
@@ -396,6 +410,25 @@ int libxl_read_file_contents(libxl_ctx *ctx, const char 
*filename,
     return e;
 }
 
+int libxl_read_file_contents(libxl_ctx *ctx, const char *filename,
+                             void **data_r, int *datalen_r)
+{
+    GC_INIT(ctx);
+    int rc;
+
+    rc = read_file_contents_core(gc, filename, data_r, datalen_r, 0);
+
+    GC_FREE;
+    return rc;
+}
+
+int libxl__read_sysfs_file_contents(libxl__gc *gc, const char *filename,
+                                   void **data_r, int *datalen_r)
+{
+    return read_file_contents_core(gc, filename, data_r, datalen_r, 1);
+}
+
+
 #define READ_WRITE_EXACTLY(rw, zero_is_eof, constdata)                    \
                                                                           \
   int libxl_##rw##_exactly(libxl_ctx *ctx, int fd,                 \
-- 
2.1.4


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