[PATCH v6] server: Implement file access hints using posix_fadvise

[Luke Deller]

Implement file access pattern hints for sequential or random file access
using posix_fadvise if available.  On Linux this will influence the
kernel's readahead behaviour.

Signed-off-by: Luke Deller 
---
v6: Use a configure check rather than _POSIX_C_SOURCE macro check to see
if posix_fadvise is available
---
 configure    |  1 +
 configure.ac |  1 +
 server/fd.c  | 10 ++++++++++
 3 files changed, 12 insertions(+)

diff --git a/configure b/configure
index cc4f64347f1..3197f07f02b 100755
--- a/configure
+++ b/configure
@@ -18010,6 +18010,7 @@ for ac_func in \
    pipe2 \
    poll \
    port_create \
+	posix_fadvise \
    prctl \
    pread \
    proc_pidinfo \
diff --git a/configure.ac b/configure.ac
index cb8fa573c37..361da0428cf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2186,6 +2186,7 @@ AC_CHECK_FUNCS(\
    pipe2 \
    poll \
    port_create \
+	posix_fadvise \
    prctl \
    pread \
    proc_pidinfo \
diff --git a/server/fd.c b/server/fd.c
index de7c5d7e36d..7c101fde2e0 100644
--- a/server/fd.c
+++ b/server/fd.c
@@ -1882,6 +1882,7 @@ struct fd *open_fd( struct fd *root, const char *name, struct unicode_str nt_nam
     int root_fd = -1;
     int rw_mode;
     char *path;
+    unsigned int cache_hint;

if (((options & FILE_DELETE_ON_CLOSE) && !(access & DELETE)) ||
         ((options & FILE_DIRECTORY_FILE) && (flags & O_TRUNC)))
@@ -2026,6 +2027,15 @@ struct fd *open_fd( struct fd *root, const char *name, struct unicode_str nt_nam
         free( closed_fd );
         fd->cacheable = 1;
     }
+
+#ifdef HAVE_POSIX_FADVISE
+    cache_hint = options & (FILE_SEQUENTIAL_ONLY | FILE_RANDOM_ACCESS);
+    if (cache_hint == FILE_SEQUENTIAL_ONLY)
+        posix_fadvise( fd->unix_fd, 0, 0, POSIX_FADV_SEQUENTIAL );
+    else if (cache_hint == FILE_RANDOM_ACCESS)
+        posix_fadvise( fd->unix_fd, 0, 0, POSIX_FADV_RANDOM );
+#endif
+
     if (root_fd != -1) fchdir( server_dir_fd ); /* go back to the server dir */
     return fd;