xmalloc_open_read_close: use fstat to get file size (instead of lseek).

by Joakim Tjernlund <Joakim.Tjernlund AT transmode.se>

function                                             old     new   delta
xmalloc_open_read_close                              190     181      -9

1 files changed, 43 insertions, 0 deletions

diff --git a/libbb/read.c b/libbb/read.c
index e5f140f3b..288358d79 100644
--- a/libbb/read.c
+++ b/libbb/read.c
@@ -211,6 +211,48 @@ void *xmalloc_open_read_close(const char *filename, size_t *sizep)
         size_t size;
         int fd;
         off_t len;
+        struct stat st;
+
+        fd = open(filename, O_RDONLY);
+        if (fd < 0)
+                return NULL;
+
+        st.st_size = 0; /* in case fstat fail, define to 0 */
+        fstat(fd, &st);
+        /* /proc/N/stat files report len 0 here */
+        /* In order to make such files readable, we add small const */
+        len = st.st_size | 0x3ff; /* read only 1k on unseekable files */
+        size = sizep ? *sizep : INT_MAX;
+        if (len < size)
+                size = len;
+        buf = xmalloc(size + 1);
+        size = read_close(fd, buf, size);
+        if ((ssize_t)size < 0) {
+                free(buf);
+                return NULL;
+        }
+        xrealloc(buf, size + 1);
+        buf[size] = '\0';
+
+        if (sizep)
+                *sizep = size;
+        return buf;
+}
+
+#ifdef USING_LSEEK_TO_GET_SIZE
+/* Alternatively, file size can be obtained by lseek to the end.
+ * The code is slightly bigger. Retained in case fstat approach
+ * will not work for some weird cases (/proc, block devices, etc).
+ * (NB: lseek also can fail to work for some weird files) */
+
+// Read (potentially big) files in one go. File size is estimated by
+// lseek to end.
+void *xmalloc_open_read_close(const char *filename, size_t *sizep)
+{
+        char *buf;
+        size_t size;
+        int fd;
+        off_t len;
 
         fd = open(filename, O_RDONLY);
         if (fd < 0)
@@ -240,6 +282,7 @@ void *xmalloc_open_read_close(const char *filename, size_t *sizep)
                 *sizep = size;
         return buf;
 }
+#endif
 
 void *xmalloc_xopen_read_close(const char *filename, size_t *sizep)
 {