main.c: Use fstat(2) on move_file

This allows to reuse the same file descriptor to both open(2) and
fstat(2) the file.

1 files changed, 30 insertions, 24 deletions

diff --git a/main.c b/main.c
index d76b225..cdb1aed 100644
--- a/main.c
+++ b/main.c
@@ -1057,23 +1057,23 @@ end:
 static int move_file(const char *const old, const char *const new)
 {
     int ret = -1;
-    FILE *const f = fopen(old, "rb");
-    const int fd = open(new, O_WRONLY | O_CREAT, 0600);
+    const int fd_old = open(old, O_RDONLY),
+        fd_new = open(new, O_WRONLY | O_CREAT, 0600);
     struct stat sb;
 
-    if (!f)
+    if (fd_old < 0)
     {
-        fprintf(stderr, "%s: fopen(3): %s\n", __func__, strerror(errno));
+        fprintf(stderr, "%s: open(2) fd_old: %s\n", __func__, strerror(errno));
         goto end;
     }
-    else if (fd < 0)
+    else if (fd_new < 0)
     {
         fprintf(stderr, "%s: open(2): %s\n", __func__, strerror(errno));
         goto end;
     }
-    else if (stat(old, &sb))
+    else if (fstat(fd_old, &sb))
     {
-        fprintf(stderr, "%s: stat(2): %s\n", __func__, strerror(errno));
+        fprintf(stderr, "%s: fstat(2): %s\n", __func__, strerror(errno));
         goto end;
     }
 
@@ -1082,24 +1082,30 @@ static int move_file(const char *const old, const char *const new)
         char buf[BUFSIZ];
         const off_t left = sb.st_size - i;
         const size_t rem = left > sizeof buf ? sizeof buf : left;
-        ssize_t w;
+        const ssize_t r = read(fd_old, buf, rem);
 
-        if (!fread(buf, rem, 1, f))
-        {
-            fprintf(stderr, "%s: fread(3) failed, feof=%d, ferror=%d\n",
-                __func__, feof(f), ferror(f));
-            goto end;
-        }
-        else if ((w = write(fd, buf, rem)) < 0)
+        if (r < 0)
         {
-            fprintf(stderr, "%s: write(2): %s\n", __func__, strerror(errno));
+            fprintf(stderr, "%s: read(2): %s\n", __func__, strerror(errno));
             goto end;
         }
-        else if (w != rem)
+
+        size_t wrem = r;
+        const void *p = buf;
+
+        while (wrem)
         {
-            fprintf(stderr, "%s: write(2): expected to write %zu bytes, "
-                "only %ju written\n", __func__, rem, (intmax_t)w);
-            goto end;
+            const ssize_t w = write(fd_new, p, wrem);
+
+            if (w < 0)
+            {
+                fprintf(stderr, "%s: write(2): %s\n",
+                    __func__, strerror(errno));
+                goto end;
+            }
+
+            p = (const char *)p + w;
+            wrem -= w;
         }
 
         i += rem;
@@ -1108,15 +1114,15 @@ static int move_file(const char *const old, const char *const new)
     ret = 0;
 
 end:
-    if (fd >= 0 && close(fd))
+    if (fd_old >= 0 && close(fd_old))
     {
-        fprintf(stderr, "%s: close(2): %s\n", __func__, strerror(errno));
+        fprintf(stderr, "%s: close(2) fd_old: %s\n", __func__, strerror(errno));
         ret = -1;
     }
 
-    if (f && fclose(f))
+    if (fd_new >= 0 && close(fd_new))
     {
-        fprintf(stderr, "%s: fclose(3): %s\n", __func__, strerror(errno));
+        fprintf(stderr, "%s: close(2) fd_new: %s\n", __func__, strerror(errno));
         ret = -1;
     }