2:25 p.m.
In several places where asynch handlers manually call the provided
nbd_completion_callback, the value of errno is indeterminate (for
example, in file-ops.c:file_asynch_read(), the previous call to
file_synch_read() already triggered exit() on error, but does not
guarantee what is left in errno on success). As the callback should
be paying attention to the value of *error (to be fixed in the next
patch), we are better off ensuring that we pass in a pointer to a
known-zero value; at which point, it is easier to use a dummy variable
on the stack than to mess around with errno and it's magic macro
expansion into a thread-local storage location.
Note that several callsites then check if the callback returned -1,
and if so assume that the callback has caused errno to now have a sane
value to pass on to perror. In theory, the fact that we are no longer
passing in &errno means that if the callback assigns into *error but
did not otherwise affect errno, our perror call would no longer
reflect that value. But in practice, since the callback never
actually returned -1, nor even assigned into *error, the call to
perror is dead code; although I have chosen to defer that additional
cleanup to the next patch.
---
copy/file-ops.c | 17 ++++++++++-------
copy/multi-thread-copying.c | 8 +++++---
copy/null-ops.c | 12 +++++++-----
3 files changed, 22 insertions(+), 15 deletions(-)
diff --git a/copy/file-ops.c b/copy/file-ops.c
index 84704341..e37a5014 100644
--- a/copy/file-ops.c
+++ b/copy/file-ops.c
@@ -1,5 +1,5 @@
/* NBD client library in userspace.
- * Copyright (C) 2020 Red Hat Inc.
+ * Copyright (C) 2020-2022 Red Hat Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
@@ -587,10 +587,11 @@ file_asynch_read (struct rw *rw,
struct command *command,
nbd_completion_callback cb)
{
+ int dummy = 0;
+
file_synch_read (rw, slice_ptr (command->slice),
command->slice.len, command->offset);
- errno = 0;
- if (cb.callback (cb.user_data, &errno) == -1) {
+ if (cb.callback (cb.user_data, &dummy) == -1) {
perror (rw->name);
exit (EXIT_FAILURE);
}
@@ -601,10 +602,11 @@ file_asynch_write (struct rw *rw,
struct command *command,
nbd_completion_callback cb)
{
+ int dummy = 0;
+
file_synch_write (rw, slice_ptr (command->slice),
command->slice.len, command->offset);
- errno = 0;
- if (cb.callback (cb.user_data, &errno) == -1) {
+ if (cb.callback (cb.user_data, &dummy) == -1) {
perror (rw->name);
exit (EXIT_FAILURE);
}
@@ -614,10 +616,11 @@ static bool
file_asynch_zero (struct rw *rw, struct command *command,
nbd_completion_callback cb, bool allocate)
{
+ int dummy = 0;
+
if (!file_synch_zero (rw, command->offset, command->slice.len, allocate))
return false;
- errno = 0;
- if (cb.callback (cb.user_data, &errno) == -1) {
+ if (cb.callback (cb.user_data, &dummy) == -1) {
perror (rw->name);
exit (EXIT_FAILURE);
}
diff --git a/copy/multi-thread-copying.c b/copy/multi-thread-copying.c
index b17ca598..815b8a02 100644
--- a/copy/multi-thread-copying.c
+++ b/copy/multi-thread-copying.c
@@ -1,5 +1,5 @@
/* NBD client library in userspace.
- * Copyright (C) 2020 Red Hat Inc.
+ * Copyright (C) 2020-2022 Red Hat Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
@@ -393,6 +393,7 @@ finished_read (void *vp, int *error)
bool last_is_hole = false;
uint64_t i;
struct command *newcommand;
+ int dummy = 0;
/* Iterate over whole blocks in the command, starting on a block
* boundary.
@@ -475,7 +476,7 @@ finished_read (void *vp, int *error)
/* Free the original command since it has been split into
* subcommands and the original is no longer needed.
*/
- free_command (command, &errno);
+ free_command (command, &dummy);
}
return 1; /* auto-retires the command */
@@ -502,6 +503,7 @@ fill_dst_range_with_zeroes (struct command *command)
{
char *data;
size_t data_size;
+ int dummy = 0;
if (destination_is_zero)
goto free_and_return;
@@ -537,7 +539,7 @@ fill_dst_range_with_zeroes (struct command *command)
free (data);
free_and_return:
- free_command (command, &errno);
+ free_command (command, &dummy);
}
static int
diff --git a/copy/null-ops.c b/copy/null-ops.c
index a38666d6..11cd5116 100644
--- a/copy/null-ops.c
+++ b/copy/null-ops.c
@@ -1,5 +1,5 @@
/* NBD client library in userspace.
- * Copyright (C) 2020-2021 Red Hat Inc.
+ * Copyright (C) 2020-2022 Red Hat Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
@@ -117,8 +117,9 @@ null_asynch_write (struct rw *rw,
struct command *command,
nbd_completion_callback cb)
{
- errno = 0;
- if (cb.callback (cb.user_data, &errno) == -1) {
+ int dummy = 0;
+
+ if (cb.callback (cb.user_data, &dummy) == -1) {
perror (rw->name);
exit (EXIT_FAILURE);
}
@@ -128,8 +129,9 @@ static bool
null_asynch_zero (struct rw *rw, struct command *command,
nbd_completion_callback cb, bool allocate)
{
- errno = 0;
- if (cb.callback (cb.user_data, &errno) == -1) {
+ int dummy = 0;
+
+ if (cb.callback (cb.user_data, &dummy) == -1) {
perror (rw->name);
exit (EXIT_FAILURE);
}
--
2.34.1