Code Review: Tolerate NULL device functions

[Davide Libenzi]

It makes life easier if certain simple devices (ex, things like #version), would not have to declare empty stubs for functions it does not need to have.

https://github.com/brho/akaros/compare/master...dlibenzi:tollerate_missing_devfuncs

The following changes since commit c8a6943551e4eb433c058e258bca0a99e713d581:

  Rename backtrace_kframe -> backtrace_hwtf [2/2] (2015-12-10 11:26:40 -0500)

are available in the git repository at:

  g...@github.com:dlibenzi/akaros tollerate_missing_devfuncs

for you to fetch changes up to b2b238bfd135d435a390d36067eb472aaa4c239b:

  Allow for certain device APIs to be NULL (2015-12-15 14:42:17 -0800)

----------------------------------------------------------------

Davide Libenzi (1):

      Allow for certain device APIs to be NULL

 kern/src/ns/chan.c   | 18 ++++++++++++------

 kern/src/ns/devtab.c | 15 ++++++++++-----

 2 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/kern/src/ns/chan.c b/kern/src/ns/chan.c

index 918f289..ca2c965 100644

--- a/kern/src/ns/chan.c

+++ b/kern/src/ns/chan.c

@@ -116,16 +116,20 @@ void chandevreset(void)

 {

  int i;

 

- for (i = 0; &devtab[i] < __devtabend; i++)

- devtab[i].reset();

+ for (i = 0; &devtab[i] < __devtabend; i++) {

+ if (devtab[i].reset)

+ devtab[i].reset();

+ }

 }

 

 void chandevinit(void)

 {

  int i;

 

- for (i = 0; &devtab[i] < __devtabend; i++)

- devtab[i].init();

+ for (i = 0; &devtab[i] < __devtabend; i++) {

+ if (devtab[i].init)

+ devtab[i].init();

+ }

 }

 

 void chandevshutdown(void)

@@ -134,8 +138,10 @@ void chandevshutdown(void)

 

  /* shutdown in reverse order */

  for (i = 0; &devtab[i] < __devtabend; i++) ;

- for (i--; i >= 0; i--)

- devtab[i].shutdown();

+ for (i--; i >= 0; i--) {

+ if (devtab[i].shutdown)

+ devtab[i].shutdown();

+ }

 }

 

 static void chan_release(struct kref *kref)

diff --git a/kern/src/ns/devtab.c b/kern/src/ns/devtab.c

index 40ef1e3..7f1c5ab 100644

--- a/kern/src/ns/devtab.c

+++ b/kern/src/ns/devtab.c

@@ -20,8 +20,10 @@ void devtabreset()

 {

  int i;

 

- for (i = 0; &devtab[i] < __devtabend; i++)

- devtab[i].reset();

+ for (i = 0; &devtab[i] < __devtabend; i++) {

+ if (devtab[i].reset)

+ devtab[i].reset();

+ }

 }

 

 void devtabinit()

@@ -32,7 +34,8 @@ void devtabinit()

  /* if we have errors, check the align of struct dev and objdump */

  printd("i %d, '%s', dev %p, init %p\n", i, devtab[i].name,

  &devtab[i], devtab[i].init);

- devtab[i].init();

+ if (devtab[i].init)

+ devtab[i].init();

  }

 }

 

@@ -44,8 +47,10 @@ void devtabshutdown()

  * Shutdown in reverse order.

  */

  for (i = 0; &devtab[i] < __devtabend; i++) ;

- for (i--; i >= 0; i--)

- devtab[i].shutdown();

+ for (i--; i >= 0; i--) {

+ if (devtab[i].shutdown)

+ devtab[i].shutdown();

+ }

 }

 

 struct dev *devtabget(const char *name, int user)

[Barret Rhoden]

On 2015-12-15 at 14:45 "'Davide Libenzi' via Akaros"

<aka...@googlegroups.com> wrote:
> It makes life easier if certain simple devices (ex, things like
> #version), would not have to declare empty stubs for functions it
> does not need to have.

Under the old system (right before this patch), #version didn't need
to have stubs (like ver_init and ver_shutdown). It can just use
devinit, devshutdown, and devreset. But I prefer allowing them to be
0, since it was a source of confusion.

Merged to master at 345158006a10..f945c3bf7870 (from, to]

You can see the entire diff with 'git diff' or at
https://github.com/brho/akaros/compare/345158006a10...f945c3bf7870

Barret

[Davide Libenzi]

In Linux, the file_ops, can just be initialized with only the callbacks you want to override.

If we want to always have the devtab struct to hold valid callbacks, we could have a DEVTAB_INIT macro, which initializes to the defaults, followed by device specific initializations.

As this is allowed in GCC:

struc a {

  .close = dummy_close,

  ...

  .close = my_device_close

};

Barret

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