From 76b4c5001ead337d3cb221b65488998ed2589afb Mon Sep 17 00:00:00 2001
From: Victor Polevoy <fx@thefx.co>
Date: Mon, 14 Jul 2025 18:51:27 +0200
Subject: [PATCH] Use shmem instead of a buffer

---
 pgxn/neon/communicator/src/neon_request.rs |  4 +--
 pgxn/neon/communicator_new.c               | 30 +++++++++++-----------
 2 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/pgxn/neon/communicator/src/neon_request.rs b/pgxn/neon/communicator/src/neon_request.rs
index 20f896651d..98bdbb8822 100644
--- a/pgxn/neon/communicator/src/neon_request.rs
+++ b/pgxn/neon/communicator/src/neon_request.rs
@@ -190,13 +190,13 @@ pub struct CReadSlruSegmentRequest {
     pub request_lsn: CLsn,
     /// Must be a null-terminated C string containing **absolute**
     /// file path.
-    pub destination_file_path: [std::ffi::c_char; libc::PATH_MAX as usize],
+    pub destination_file_path: ShmemBuf,
 }
 
 impl CReadSlruSegmentRequest {
     /// Returns the path to the file where the segment is read into.
     pub(crate) fn destination_file_path(&self) -> String {
-        unsafe { CStr::from_ptr(self.destination_file_path.as_ptr()) }
+        unsafe { CStr::from_ptr(self.destination_file_path.as_mut_ptr() as *const _) }
             .to_string_lossy()
             .into_owned()
     }
diff --git a/pgxn/neon/communicator_new.c b/pgxn/neon/communicator_new.c
index b14fd5a9f8..a7225e78e7 100644
--- a/pgxn/neon/communicator_new.c
+++ b/pgxn/neon/communicator_new.c
@@ -1021,28 +1021,28 @@ communicator_new_read_slru_segment(
 	}
 
 	// Scoping should help deallocate the absolute path buffer.
-	{
-		char abs_path[PATH_MAX];
+	char *abs_path = bounce_buf();
 
-		if (path[0] != '/') {
-			char cwd[PATH_MAX];
-			getcwd(cwd, sizeof(cwd));
+	if (path[0] != '/') {
+		char cwd[PATH_MAX];
+		getcwd(cwd, sizeof(cwd));
 
-			const int size = snprintf(NULL, 0, "%s/%s", cwd, path);
-			if (size < 0 || size >= PATH_MAX) {
-				elog(ERROR, "read_slru_segment failed to create an absolute path for \"%s\"", path);
-				return -1;
-			}
+		const int size = snprintf(NULL, 0, "%s/%s", cwd, path);
 
-			snprintf(abs_path, size + 1, "%s/%s", cwd, path);
-		} else {
-			strncpy(abs_path, path, sizeof(abs_path));
+		if (size < 0 || size >= PATH_MAX) {
+			elog(ERROR, "read_slru_segment failed to create an absolute path for \"%s\"", path);
+			return -1;
 		}
-		strncpy(request.read_slru_segment.destination_file_path, abs_path, sizeof(request.read_slru_segment.destination_file_path));
+
+		snprintf(abs_path, size + 1, "%s/%s", cwd, path);
+	} else {
+		strncpy(abs_path, path, sizeof(abs_path));
 	}
 
+	request.read_slru_segment.destination_file_path.ptr = abs_path;
+
 	elog(DEBUG5, "readslrusegment called for kind=%u, segno=%u, file_path=\"%s\"",
-		kind, segno, request.read_slru_segment.destination_file_path);
+		kind, segno, request.read_slru_segment.destination_file_path.ptr);
 
 	/* FIXME: see `request_lsns` in main_loop.rs for why this is needed */
 	XLogSetAsyncXactLSN(request_lsns->request_lsn);