stream_file: use fstat() instead of lseek() to determine file size

It appears using lseek() to seek to the end and back to determine file
size is inefficient in some cases.

With CIFS, this restores the performance regression that happened when
the stream cache was removed (which called read() from a thread). This
is probably faster than the old code too, because it's the seeking that
was slowing down CIFS.

According to the user who tested this, the size caching does not help
with fstat() (although it did with the old method).

Fixes: #7408, #7152

1 files changed, 8 insertions, 3 deletions

diff --git a/stream/stream_file.c b/stream/stream_file.c
index 6e69f33c94..9f83b73dd1 100644
--- a/stream/stream_file.c
+++ b/stream/stream_file.c
@@ -77,9 +77,14 @@ static int64_t get_size(stream_t *s)
 {
     struct priv *p = s->priv;
     if (p->cached_size == -2) {
-        off_t size = lseek(p->fd, 0, SEEK_END);
-        lseek(p->fd, s->pos, SEEK_SET);
-        p->cached_size = size < 0 ? -1 : size;
+        int64_t size = -1;
+        struct stat st;
+        if (fstat(p->fd, &st) == 0) {
+            if (st.st_size <= 0 && !s->seekable)
+                st.st_size = -1;
+            size = st.st_size < 0 ? -1 : st.st_size;
+        }
+        p->cached_size = size;
     }
     return p->cached_size;
 }