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Date: Wed, 30 Nov 2022 20:43:09 +0000
From: Eric Wong <e@80x24.org>
To: mwrap-perl@80x24.org
Subject: Re: [PATCH 1/2] use file-backed mmap on Linux
Message-ID: <20221130204309.GA30076@dcvr>
References: <20221130064930.5239-1-e@80x24.org>
 <20221130064930.5239-2-e@80x24.org>
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Eric Wong <e@80x24.org> wrote:
> +	fd = open(tmpdir, O_TMPFILE|O_RDWR|S_IRUSR);
> +	if (fd < 0) {
> +		flags |= MAP_ANONYMOUS;
> +	} else {
> +		ssize_t w = pwrite(fd, "", 1, size - 1); /* sparse file */
> +
> +		if (w < 0)
> +			flags |= MAP_ANONYMOUS;
> +	}

Will squash this to better handle pwrite errors and short writes
(likely due to ENOSPC):

diff --git a/mymalloc.h b/mymalloc.h
index f5a171e..88190d5 100644
--- a/mymalloc.h
+++ b/mymalloc.h
@@ -52,8 +52,11 @@ static void *my_mmap(size_t size)
 	} else {
 		ssize_t w = pwrite(fd, "", 1, size - 1); /* sparse file */
 
-		if (w < 0)
+		if (w <= 0) { /* 0 may be ENOSPC */
 			flags |= MAP_ANONYMOUS;
+			close(fd);
+			fd = -1;
+		}
 	}
 	ret = mmap(NULL, size, PROT_READ|PROT_WRITE, flags, fd, 0);
 	if (fd >= 0) {