reorderbuffer: preserve errno while reporting error

Clobbering errno during cleanup after an error is an oft-repeated, easy
to make mistake.  Deal with it here as everywhere else, by saving it
aside and restoring after cleanup, before ereport'ing.

In passing, add a missing errcode declaration in another ereport() call
in the same file, which I noticed while skimming the file looking for
similar problems.

Backpatch to 9.4, where this code was introduced.

diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 30aa5706d881c14b30a3bf218b1e795ad32104d4..3b63e21dbd0a7c0b1053fd412915e9c25000f0c4 100644 (file)
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -2136,7 +2136,10 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 
    if (write(fd, rb->outbuf, ondisk->size) != ondisk->size)
    {
+       int save_errno = errno;
+
        CloseTransientFile(fd);
+       errno = save_errno;
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not write to data file for XID %u: %m",
@@ -2865,7 +2868,8 @@ ApplyLogicalMappingFile(HTAB *tuplecid_data, Oid relid, const char *fname)
    fd = OpenTransientFile(path, O_RDONLY | PG_BINARY, 0);
    if (fd < 0)
        ereport(ERROR,
-               (errmsg("could not open file \"%s\": %m", path)));
+               (errcode_for_file_access(),
+                errmsg("could not open file \"%s\": %m", path)));
 
    while (true)
    {