[PATCH 0/2] chardev/char-mux: tweak mux bitset operations

[PATCH 0/2] chardev/char-mux: tweak mux bitset operations

[Roman Penyaev]

Patchset tweaks bitset operations by changing a constant to unsigned
long, introduces a static compile check and simplifies bitset operations.

Roman Penyaev (2):
  chardev/char-mux: shift unsigned long to avoid 32-bit overflow
  chardev/char-mux: make boolean bit check instead of find_next_bit()

 chardev/char-mux.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Clément Mathieu--Drif <clement.mathieu--drif@eviden.com>
Cc: qemu-devel@nongnu.org

-- 
2.34.1

[PATCH 1/2] chardev/char-mux: shift unsigned long to avoid 32-bit overflow

[Roman Penyaev]

Allthough the size of MAX_MUX is equal to 4 and likely will never
change, this patch changes type of constant to unsigned long to
be on the safe side.

Also add a static compile check that MAX_MUX never bigger than
`sizeof(d->mux_bitset)`.

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Clément Mathieu--Drif <clement.mathieu--drif@eviden.com>
Cc: qemu-devel@nongnu.org
---
 chardev/char-mux.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/chardev/char-mux.c b/chardev/char-mux.c
index bda5c45e6058..355520714979 100644
--- a/chardev/char-mux.c
+++ b/chardev/char-mux.c
@@ -316,6 +316,8 @@ bool mux_chr_attach_frontend(MuxChardev *d, CharBackend *b,
 {
     unsigned int bit;
 
+    QEMU_BUILD_BUG_ON(MAX_MUX > sizeof(d->mux_bitset));
+
     bit = find_next_zero_bit(&d->mux_bitset, MAX_MUX, 0);
     if (bit >= MAX_MUX) {
         error_setg(errp,
@@ -325,7 +327,7 @@ bool mux_chr_attach_frontend(MuxChardev *d, CharBackend *b,
         return false;
     }
 
-    d->mux_bitset |= (1 << bit);
+    d->mux_bitset |= (1ul << bit);
     d->backends[bit] = b;
     *tag = bit;
 
@@ -341,7 +343,7 @@ bool mux_chr_detach_frontend(MuxChardev *d, unsigned int tag)
         return false;
     }
 
-    d->mux_bitset &= ~(1 << bit);
+    d->mux_bitset &= ~(1ul << bit);
     d->backends[bit] = NULL;
 
     return true;
-- 
2.34.1

[PATCH 2/2] chardev/char-mux: make boolean bit check instead of find_next_bit()

[Roman Penyaev]

This patch simplifies (and makes less confusing) bit checks by
replacing `find_next_bit()` calls with boolean AND operation.

Resolves: Coverity CID 1563776
Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Clément Mathieu--Drif <clement.mathieu--drif@eviden.com>
Cc: qemu-devel@nongnu.org
---
 chardev/char-mux.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/chardev/char-mux.c b/chardev/char-mux.c
index 355520714979..f613a22e3758 100644
--- a/chardev/char-mux.c
+++ b/chardev/char-mux.c
@@ -336,15 +336,12 @@ bool mux_chr_attach_frontend(MuxChardev *d, CharBackend *b,
 
 bool mux_chr_detach_frontend(MuxChardev *d, unsigned int tag)
 {
-    unsigned int bit;
-
-    bit = find_next_bit(&d->mux_bitset, MAX_MUX, tag);
-    if (bit != tag) {
+    if (!(d->mux_bitset & (1ul << tag))) {
         return false;
     }
 
-    d->mux_bitset &= ~(1ul << bit);
-    d->backends[bit] = NULL;
+    d->mux_bitset &= ~(1ul << tag);
+    d->backends[tag] = NULL;
 
     return true;
 }
@@ -353,7 +350,7 @@ void mux_set_focus(Chardev *chr, unsigned int focus)
 {
     MuxChardev *d = MUX_CHARDEV(chr);
 
-    assert(find_next_bit(&d->mux_bitset, MAX_MUX, focus) == focus);
+    assert(d->mux_bitset & (1ul << focus));
 
     if (d->focus != -1) {
         mux_chr_send_event(d, d->focus, CHR_EVENT_MUX_OUT);
-- 
2.34.1

Re: [PATCH 0/2] chardev/char-mux: tweak mux bitset operations

[Marc-André Lureau]

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Hi

On Sat, Nov 2, 2024 at 3:11 PM Roman Penyaev <r.peniaev@gmail.com> wrote:

> Patchset tweaks bitset operations by changing a constant to unsigned
> long, introduces a static compile check and simplifies bitset operations.
>
> Roman Penyaev (2):
>   chardev/char-mux: shift unsigned long to avoid 32-bit overflow
>   chardev/char-mux: make boolean bit check instead of find_next_bit()
>
>  chardev/char-mux.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
>
> Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
> Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: Clément Mathieu--Drif <clement.mathieu--drif@eviden.com>
> Cc: qemu-devel@nongnu.org


Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>


-- 
Marc-André Lureau

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Re: [PATCH 0/2] chardev/char-mux: tweak mux bitset operations

[CLEMENT MATHIEU--DRIF]

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Hi Roman,

Reviewed-by Clément Mathieu--Drif <clement.mathieu--drif@eviden.com><mailto:clement.mathieu--drif@eviden.com> Thanks!

On 02/11/2024 12:07, Roman Penyaev wrote:

Caution: External email. Do not open attachments or click links, unless this email comes from a known sender and you know the content is safe.


Patchset tweaks bitset operations by changing a constant to unsigned
long, introduces a static compile check and simplifies bitset operations.

Roman Penyaev (2):
  chardev/char-mux: shift unsigned long to avoid 32-bit overflow
  chardev/char-mux: make boolean bit check instead of find_next_bit()

 chardev/char-mux.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com><mailto:r.peniaev@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com><mailto:marcandre.lureau@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org><mailto:peter.maydell@linaro.org>
Cc: Clément Mathieu--Drif <clement.mathieu--drif@eviden.com><mailto:clement.mathieu--drif@eviden.com>
Cc: qemu-devel@nongnu.org<mailto:qemu-devel@nongnu.org>

--
2.34.1




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