Re: [kvm-unit-tests PATCH v3 3/6] s390x: Add linemode buffer to fix newline on every print

Janosch Frank
2019-09-20T08:31:53Z

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On 9/20/19 10:24 AM, David Hildenbrand wrote:
> On 20.09.19 10:03, Janosch Frank wrote:
>> Linemode seems to add a newline for each sent message which makes
>> reading rather hard. Hence we add a small buffer and only print if
>> it's full or a newline is encountered. Except for when the string is
>> longer than the buffer, then we flush the buffer and print directly.
>
> I think that last sentence is not correct anymore.
>
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> Reviewed-by: Thomas Huth <thuth@redhat.com>
>> Acked-by: David Hildenbrand <david@redhat.com>
>> ---
>> lib/s390x/sclp-console.c | 45 ++++++++++++++++++++++++++++++++++++----
>> 1 file changed, 41 insertions(+), 4 deletions(-)
>>
>> diff --git a/lib/s390x/sclp-console.c b/lib/s390x/sclp-console.c
>> index 19416b5..e1b9000 100644
>> --- a/lib/s390x/sclp-console.c
>> +++ b/lib/s390x/sclp-console.c
>> @@ -13,6 +13,7 @@
>> #include <asm/page.h>
>> #include <asm/arch_def.h>
>> #include <asm/io.h>
>> +#include <asm/spinlock.h>
>> #include "sclp.h"
>>
>> /*
>> @@ -87,6 +88,10 @@ static uint8_t _ascebc[256] = {
>> 0x90, 0x3F, 0x3F, 0x3F, 0x3F, 0xEA, 0x3F, 0xFF
>> };
>>
>> +static char lm_buff[120];
>> +static unsigned char lm_buff_off;
>> +static struct spinlock lm_buff_lock;
>> +
>> static void sclp_print_ascii(const char *str)
>> {
>> int len = strlen(str);
>> @@ -103,10 +108,10 @@ static void sclp_print_ascii(const char *str)
>> sclp_service_call(SCLP_CMD_WRITE_EVENT_DATA, sccb);
>> }
>>
>> -static void sclp_print_lm(const char *str)
>> +static void lm_print(const char *buff, int len)
>> {
>> unsigned char *ptr, *end, ch;
>> - unsigned int count, offset, len;
>> + unsigned int count, offset;
>> struct WriteEventData *sccb;
>> struct mdb *mdb;
>> struct mto *mto;
>> @@ -117,11 +122,10 @@ static void sclp_print_lm(const char *str)
>> end = (unsigned char *) sccb + 4096 - 1;
>> memset(sccb, 0, sizeof(*sccb));
>> ptr = (unsigned char *) &sccb->msg.mdb.mto;
>> - len = strlen(str);
>> offset = 0;
>> do {
>> for (count = sizeof(*mto); offset < len; count++) {
>> - ch = str[offset++];
>> + ch = buff[offset++];
>> if (ch == 0x0a || ptr + count > end)
>> break;
>> ptr[count] = _ascebc[ch];
>> @@ -148,6 +152,39 @@ static void sclp_print_lm(const char *str)
>> sclp_service_call(SCLP_CMD_WRITE_EVENT_DATA, sccb);
>> }
>>
>> +
>> +/*
>> + * In contrast to the ascii console, linemode produces a new
>> + * line with every write of data. The report() function uses
>> + * several printf() calls to generate a line of data which
>> + * would all end up on different lines.
>> + *
>> + * Hence we buffer here until we encounter a \n or the buffer
>> + * is full. That means that linemode output can look a bit
>> + * different from ascii and that it takes a bit longer for
>> + * lines to appear.
>> + */
>> +static void sclp_print_lm(const char *str)
>> +{
>> + int len = strlen(str), i = 0;
>> +
>> + spin_lock(&lm_buff_lock);
>> +
>> + while (len) {
>
> for (i = 0; i < len; i++)
>
> Then make len const and drop "len--" and "i++" from the body.

Sure, the loop was a first draft anyway.
I'm asking myself how I ended up writing something so complicated in the
first place :-)

>
>> + lm_buff[lm_buff_off] = str[i];
>> + lm_buff_off++;
>
> lm_buff[lm_buff_off++] = str[i];
>
> if you feel like saving one LOC :)
>
>> + len--;
>> + /* Buffer full or newline? */
>> + if (str[i] == '\n' || lm_buff_off == (sizeof(lm_buff) - 1)) {
>
> I still prefer ARRAY_SIZE(), but this is also fine.
>
>> + lm_print(lm_buff, lm_buff_off);
>> + memset(lm_buff, 0 , sizeof(lm_buff));
>
> Is the memset really necessary? (I would have assumed it would only
> print until the last "\n" ?)

It's not, I just like clearing things

>
>> + lm_buff_off = 0;
>> + }
>> + i++;
>> + }
>
> Guess we don't care about performance, so the simple byte-based approach
> should be just fine.

;-)

>
>> + spin_unlock(&lm_buff_lock);
>> +}
>> +
>> /*
>> * SCLP needs to be initialized by setting a send and receive mask,
>> * indicating which messages the control program (we) want(s) to
>>
>
>
> I wonder if we have to implement some kind of fflush(), so we will flush
> the buffer on any abort ... but I assume we will always end printing
> with a "\n", so we don't really care.

I haven't encountered incomplete output up to now.

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