[Xen-devel] [PATCH V4 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:
  - instead of hacking lixbl_read_file_contents for sysfs file, add
    a new entry libxl_read_sysfs_file_contents to do the work.

 tools/libxl/libxl_utils.c | 24 ++++++++++++++++++++----
 tools/libxl/libxl_utils.h |  2 ++
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
index f6be2d7..d0d56c2 100644
--- a/tools/libxl/libxl_utils.c
+++ b/tools/libxl/libxl_utils.c
@@ -322,8 +322,10 @@ out:
     return rc;
 }
 
-int libxl_read_file_contents(libxl_ctx *ctx, const char *filename,
-                             void **data_r, int *datalen_r) {
+static int libxl_read_file_contents_core(libxl_ctx *ctx, const char *filename,
+                                         void **data_r, int *datalen_r,
+                                         bool is_sysfs_file)
+{
     GC_INIT(ctx);
     FILE *f = 0;
     uint8_t *data = 0;
@@ -360,15 +362,16 @@ int libxl_read_file_contents(libxl_ctx *ctx, const char 
*filename,
 
     if (stab.st_size && data_r) {
         data = malloc(datalen);
+        memset(data, 0, datalen);
         if (!data) goto xe;
 
         rs = fread(data, 1, datalen, f);
-        if (rs != datalen) {
+        if (rs != datalen && !(feof(f) && is_sysfs_file)) {
             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);
+                   filename);
             else
                 abort();
             goto xe;
@@ -396,6 +399,19 @@ 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)
+{
+    return libxl_read_file_contents_core(ctx, filename, data_r, datalen_r, 0);
+}
+
+int libxl_read_sysfs_file_contents(libxl_ctx *ctx, const char *filename,
+                                   void **data_r, int *datalen_r)
+{
+    return libxl_read_file_contents_core(ctx, filename, data_r, datalen_r, 1);
+}
+
+
 #define READ_WRITE_EXACTLY(rw, zero_is_eof, constdata)                    \
                                                                           \
   int libxl_##rw##_exactly(libxl_ctx *ctx, int fd,                 \
diff --git a/tools/libxl/libxl_utils.h b/tools/libxl/libxl_utils.h
index 1c1761d..7639662 100644
--- a/tools/libxl/libxl_utils.h
+++ b/tools/libxl/libxl_utils.h
@@ -38,6 +38,8 @@ int libxl_is_stubdom(libxl_ctx *ctx, uint32_t domid, uint32_t 
*target_domid);
 int libxl_create_logfile(libxl_ctx *ctx, const char *name, char **full_name);
 int libxl_string_to_backend(libxl_ctx *ctx, char *s, libxl_disk_backend 
*backend);
 
+int libxl_read_sysfs_file_contents(libxl_ctx *ctx, const char *filename,
+                                   void **data_r, int *datalen_r);
 int libxl_read_file_contents(libxl_ctx *ctx, const char *filename,
                              void **data_r, int *datalen_r);
   /* Reads the contents of the plain file filename into a mallocd
-- 
2.1.4


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