Attachment 1476430 Details for Bug 1615467 – [PATCH v2] tee: recover from EAGAIN returned from fwrite()

[patch] [PATCH v2] tee: recover from EAGAIN returned from fwrite()

0001-tee-recover-from-EAGAIN-returned-from-fwrite.patch (text/plain), 2.48 KB, created by Kamil Dudka on 2018-08-16 13:53:37 UTC

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Creator: Kamil Dudka

Created: 2018-08-16 13:53:37 UTC

Size: 2.48 KB

patch

obsolete

>From 97947f4fbaed4c621d1d98cb4098d16944a775e6 Mon Sep 17 00:00:00 2001
>From: Kamil Dudka <kdudka@redhat.com>
>Date: Thu, 16 Aug 2018 13:00:14 +0200
>Subject: [PATCH v2] tee: recover from EAGAIN returned from fwrite()
>
>tee expects the output descriptors to operate in blocking mode but this
>assumption might be invalidated by other programs connected to the same
>terminal, as in the following example:
>
>$ telnet ... | tee log_file
>
>telnet calls ioctl(stdin, FIONBIO, [1]), which causes the O_NONBLOCK
>flag to be set on tee's output, which is connected to the same terminal.
>
>This patch has zero impact unless EAGAIN returns from fwrite().  In that
>case we try to reset the O_NONBLOCK flag on the output file descriptor
>and retry the call to fwrite().
>---
> src/tee.c | 39 ++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 38 insertions(+), 1 deletion(-)
>
>diff --git a/src/tee.c b/src/tee.c
>index e5165de..d8b2a26 100644
>--- a/src/tee.c
>+++ b/src/tee.c
>@@ -128,6 +128,43 @@ main (int argc, char **argv)
>   exit (ok ? EXIT_SUCCESS : EXIT_FAILURE);
> }
> 
>+/* wrapper of fwrite() that tries to recover from EAGAIN caused by externally
>+   set O_NONBLOCK flag on the output file descriptor */
>+static bool
>+write_buf (const char *buf, ssize_t size, FILE *f)
>+{
>+  int fd;
>+  int flags;
>+
>+  if (fwrite (buf, size, 1, f) == 1)
>+    /* successful write */
>+    return true;
>+  if (errno != EAGAIN)
>+    /* non-recoverable write error */
>+    return false;
>+
>+  /* read file descriptor flags */
>+  fd = fileno (f);
>+  if (fd == -1)
>+    goto fail;
>+  flags = fcntl (fd, F_GETFL);
>+  if (flags == -1)
>+    goto fail;
>+
>+  /* reset the O_NONBLOCK flag on the file descriptor */
>+  flags &= ~O_NONBLOCK;
>+  if (fcntl (fd, F_SETFL, flags) == -1)
>+    goto fail;
>+
>+  /* ... and try fwrite() once again in blocking mode */
>+  return (fwrite (buf, size, 1, f) == 1);
>+
>+fail:
>+  /* preserve the original errno value in case our recovery attempt failed */
>+  errno = EAGAIN;
>+  return false;
>+}
>+
> /* Copy the standard input into each of the NFILES files in FILES
>    and into the standard output.
>    Return true if successful.  */
>@@ -191,7 +228,7 @@ tee_files (int nfiles, const char **files)
>          Standard output is the first one.  */
>       for (i = 0; i <= nfiles; i++)
>         if (descriptors[i]
>-            && fwrite (buffer, bytes_read, 1, descriptors[i]) != 1)
>+            && !write_buf (buffer, bytes_read, descriptors[i]))
>           {
>             error (0, errno, "%s", files[i]);
>             descriptors[i] = NULL;
>-- 
>1.8.3.1
>

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Attachments on bug 1615467: 1476411 | 1476430 | 1501868