From f806be87d3276fc9f672dbf43753a3c44dc26228 Mon Sep 17 00:00:00 2001
From: Ben Noordhuis <info@bnoordhuis.nl>
Date: Mon, 30 Sep 2024 21:55:34 +0200
Subject: [PATCH] linux: use IORING_OP_FTRUNCATE when available (#4554)

Route ftruncate() system calls through io_uring instead of the thread
pool when the kernel is new enough to support it (linux >= 6.9).

This commit harmonizes how libuv checks if the kernel is new enough.
Some ops were checking against `uv__kernel_version()` directly while
others stored the result of the version check as a feature flag.

Because the kernel version is cached, and because it is more direct
than a feature flag, I opted for the former approach.
---
 src/unix/fs.c       |  3 +++
 src/unix/internal.h |  2 ++
 src/unix/linux.c    | 44 +++++++++++++++++++++++++++-----------------
 src/uv-common.h     |  1 -
 4 files changed, 32 insertions(+), 18 deletions(-)

diff --git a/src/unix/fs.c b/src/unix/fs.c
index 6d810deb..d555491a 100644
--- a/src/unix/fs.c
+++ b/src/unix/fs.c
@@ -1910,6 +1910,9 @@ int uv_fs_ftruncate(uv_loop_t* loop,
   INIT(FTRUNCATE);
   req->file = file;
   req->off = off;
+  if (cb != NULL)
+    if (uv__iou_fs_ftruncate(loop, req))
+      return 0;
   POST;
 }
 
diff --git a/src/unix/internal.h b/src/unix/internal.h
index 529c783e..138685c9 100644
--- a/src/unix/internal.h
+++ b/src/unix/internal.h
@@ -344,6 +344,7 @@ int uv__random_sysctl(void* buf, size_t buflen);
 /* io_uring */
 #ifdef __linux__
 int uv__iou_fs_close(uv_loop_t* loop, uv_fs_t* req);
+int uv__iou_fs_ftruncate(uv_loop_t* loop, uv_fs_t* req);
 int uv__iou_fs_fsync_or_fdatasync(uv_loop_t* loop,
                                   uv_fs_t* req,
                                   uint32_t fsync_flags);
@@ -362,6 +363,7 @@ int uv__iou_fs_symlink(uv_loop_t* loop, uv_fs_t* req);
 int uv__iou_fs_unlink(uv_loop_t* loop, uv_fs_t* req);
 #else
 #define uv__iou_fs_close(loop, req) 0
+#define uv__iou_fs_ftruncate(loop, req) 0
 #define uv__iou_fs_fsync_or_fdatasync(loop, req, fsync_flags) 0
 #define uv__iou_fs_link(loop, req) 0
 #define uv__iou_fs_mkdir(loop, req) 0
diff --git a/src/unix/linux.c b/src/unix/linux.c
index 2f726294..803a9a9d 100644
--- a/src/unix/linux.c
+++ b/src/unix/linux.c
@@ -148,6 +148,7 @@ enum {
   UV__IORING_OP_MKDIRAT = 37,
   UV__IORING_OP_SYMLINKAT = 38,
   UV__IORING_OP_LINKAT = 39,
+  UV__IORING_OP_FTRUNCATE = 55,
 };
 
 enum {
@@ -160,10 +161,6 @@ enum {
   UV__IORING_SQ_CQ_OVERFLOW = 2u,
 };
 
-enum {
-  UV__MKDIRAT_SYMLINKAT_LINKAT = 1u,
-};
-
 struct uv__io_cqring_offsets {
   uint32_t head;
   uint32_t tail;
@@ -607,10 +604,6 @@ static void uv__iou_init(int epollfd,
   iou->sqelen = sqelen;
   iou->ringfd = ringfd;
   iou->in_flight = 0;
-  iou->flags = 0;
-
-  if (kernel_version >= /* 5.15.0 */ 0x050F00)
-    iou->flags |= UV__MKDIRAT_SYMLINKAT_LINKAT;
 
   if (no_sqarray)
     return;
@@ -871,6 +864,26 @@ int uv__iou_fs_close(uv_loop_t* loop, uv_fs_t* req) {
 }
 
 
+int uv__iou_fs_ftruncate(uv_loop_t* loop, uv_fs_t* req) {
+  struct uv__io_uring_sqe* sqe;
+  struct uv__iou* iou;
+
+  if (uv__kernel_version() < /* 6.9 */0x060900)
+    return 0;
+
+  iou = &uv__get_internal_fields(loop)->iou;
+  sqe = uv__iou_get_sqe(iou, loop, req);
+  if (sqe == NULL)
+    return 0;
+
+  sqe->fd = req->file;
+  sqe->len = req->off;
+  sqe->opcode = UV__IORING_OP_FTRUNCATE;
+  uv__iou_submit(iou);
+
+  return 1;
+}
+
 int uv__iou_fs_fsync_or_fdatasync(uv_loop_t* loop,
                                   uv_fs_t* req,
                                   uint32_t fsync_flags) {
@@ -900,11 +913,10 @@ int uv__iou_fs_link(uv_loop_t* loop, uv_fs_t* req) {
   struct uv__io_uring_sqe* sqe;
   struct uv__iou* iou;
 
-  iou = &uv__get_internal_fields(loop)->iou;
-
-  if (!(iou->flags & UV__MKDIRAT_SYMLINKAT_LINKAT))
+  if (uv__kernel_version() < /* 5.15.0 */0x050F00)
     return 0;
 
+  iou = &uv__get_internal_fields(loop)->iou;
   sqe = uv__iou_get_sqe(iou, loop, req);
   if (sqe == NULL)
     return 0;
@@ -925,11 +937,10 @@ int uv__iou_fs_mkdir(uv_loop_t* loop, uv_fs_t* req) {
   struct uv__io_uring_sqe* sqe;
   struct uv__iou* iou;
 
-  iou = &uv__get_internal_fields(loop)->iou;
-
-  if (!(iou->flags & UV__MKDIRAT_SYMLINKAT_LINKAT))
+  if (uv__kernel_version() < /* 5.15.0 */0x050F00)
     return 0;
 
+  iou = &uv__get_internal_fields(loop)->iou;
   sqe = uv__iou_get_sqe(iou, loop, req);
   if (sqe == NULL)
     return 0;
@@ -993,11 +1004,10 @@ int uv__iou_fs_symlink(uv_loop_t* loop, uv_fs_t* req) {
   struct uv__io_uring_sqe* sqe;
   struct uv__iou* iou;
 
-  iou = &uv__get_internal_fields(loop)->iou;
-
-  if (!(iou->flags & UV__MKDIRAT_SYMLINKAT_LINKAT))
+  if (uv__kernel_version() < /* 5.15.0 */0x050F00)
     return 0;
 
+  iou = &uv__get_internal_fields(loop)->iou;
   sqe = uv__iou_get_sqe(iou, loop, req);
   if (sqe == NULL)
     return 0;
diff --git a/src/uv-common.h b/src/uv-common.h
index 60bd0087..4baede2e 100644
--- a/src/uv-common.h
+++ b/src/uv-common.h
@@ -414,7 +414,6 @@ struct uv__iou {
   size_t sqelen;
   int ringfd;
   uint32_t in_flight;
-  uint32_t flags;
 };
 #endif  /* __linux__ */