I'm new to using the gwan server(link) and for that matter programming in c. I wanted to know what was the easiest way to use mysql in a c script for the gwan server?
I've experimented with dbi.c as used here and the project page can be found here, but also found that there is a c API for mysql itself which you can find here.
Anyone have experience using either or both? What are some of the pros/cons? Are there other libraries that make connecting to mysql easy for a noob like myself?
Any help appreciated.
Thanks!
[EDIT]
Also is libdbi thread safe? it appears to not be.
[EDIT 2]
It appears that the mysql lib itself is the easy way to go unless you think might be switching database types later as libdbi appears to be able to have different drivers which is nice for abstraction.
Relating to GWAN for me if i had any "mysql code" in the main function of a handler it appeared to be unsafe and caused random errors intermittently, but if i put the "mysql code" in the init function and put any data i need in a kv store accessed off of one of the global pointers the random errors went away completely. (I was using libdbi i assume it would be the same for the mysql api)
Hope this helps
I always prefer using the native c api...
#pragma link "/usr/lib/libmysqlclient.so"
#include "gwan.h"
#include <mysql/mysql.h>
int
main (int argc, char **argv)
{
MYSQL_RES *result;
MYSQL_ROW row;
MYSQL conn, *conn_h;
conn_h = mysql_init (&conn);
if (!conn_h)
{
return 200;
}
if (!mysql_real_connect (conn_h, "localhost", ctx->usr, ctx->psw, NULL, 0, NULL, 0))
{
mysql_close (conn_h);
return 200;
}
mysql_select_db (conn_h, "");
char *query = "";
if (mysql_query (conn_h, query))
{
mysql_close (conn_h);
return 200;
}
result = mysql_store_result (conn_h);
if (!result)
{
mysql_close (conn_h);
return 200;
}
if (mysql_num_rows (result) == 0)
{
return 200;
}
while ((row = mysql_fetch_row (result)))
{
/* do something with row[i] */
}
mysql_free_result (result);
mysql_close (conn_h);
return 200; // Ok
}
Keep in mind you need to initialize the mysql library if you plan to spawn threads (this code is not thread safe).
Hope this help you someway.
Related
I am new to programming and I am trying to read a page (64Bytes) from an SPI Eeprom and I got it working when reading to an array[67] (3 transmitted Bytes to start the read process via SPI + 64 Bytes data).
I am using IAR Workbench working on a STM32L475.
When I try to use pointers it does not work, probably a stupid no brainer of a beginners mistake, but I appreciate some help to solve this.
I am using a union like this (I know I am wasting mem but for the test it is like this):
//Production Data union
union Production_Data_union
{
struct
{
uint8_t Dummy_Array[3];
char Xxxx_Sn[16];
char Yyyy_Sn[16];
char Prod_Date[8];
char Firmware_Ver[8];
};
uint8_t Eeprom_Page0_Buffer[67];
};
union Production_Data_union Prod_Data;
uint8_t *Eeprom_Page0_Ptr;
uint8_t Read_Cmd[3] = {0x03, 0x00, 0x00};
uint8_t Buff[67];
uint8_t Eeprom_Page_Size = 64;
void Eeprom_Page_Read(uint8_t *Data, uint8_t Page_No);
My Main looks like this:
Eeprom_Page0_Ptr = (uint8_t*)&Prod_Data.Eeprom_Page0_Buffer;
Eeprom_Page_Read(Eeprom_Page0_Ptr, 0);
The Eeprom_Page_Read function:
void Eeprom_Page_Read(uint8_t *Data, uint8_t Page_No)
{
uint16_t Address;
Address = Page_No * Eeprom_Page_Size;
Read_Cmd[2] = Address & 0xFF;
Read_Cmd[1] = (Address >> 8) & 0xFF;
//Send READ command to Eeprom
HAL_GPIO_WritePin(GPIOD, GPIO_PIN_2, GPIO_PIN_RESET);
if(HAL_SPI_TransmitReceive(&hspi3, (uint8_t*)Read_Cmd, (uint8_t *)&Data, (Eeprom_Page_Size +3), 5000) != HAL_OK)
{
Error_Handler();
}
printf("Prod_Data:\n - Xxxx SN %s\n - Yyyy SN %s\n - Prod date %s - Firmware %s\n - Cmd - %d - %d - %d\n",
Prod_Data.Xxxx_Sn,
Prod_Data.Yyyy_Sn,
Prod_Data.Prod_Date,
Prod_Data.Firmware_Ver,
Read_Cmd[0],
Read_Cmd[1],
Read_Cmd[2]);
//Wait for SPI transfer to complete
while (HAL_SPI_GetState(&hspi3) != HAL_SPI_STATE_READY)
{
}
HAL_GPIO_WritePin(GPIOD, GPIO_PIN_2, GPIO_PIN_SET);
Read_E2prom = 0;
}
I know the content of the Eeprom is ok and I can read it if I replace “&Data” with “Buff” (Array[67]) in the HAL_SPI_TransmitReceive(...) call.
Pointer value is the start address of the structure (0x20000090).
So addressing a.s.o. should be ok but the struct is empty when using a pointer.
I am mostly interested in why this does not work and a fix to this, not so much in comments like "why don't you do it like this instead, I want to learn what I have done wrong cause this approach, I believe, should work.
Please remember that I AM NEW at programming so please explain "for Dummies".
I am not sure why that is ?
The function HAL_SPI_TransmitReceive wants a pointer to know where to store the data it receives. It essentially wants an address of where to go place the bytes. In your case, according to line
void Eeprom_Page_Read(uint8_t *Data, uint8_t Page_No){...}
Data is already a pointer, because it's denoted with a *. This means that Datais a pointer pointing to some uint8_t number/array somewhere. That somewhere is where you want your SPI to write to.
When you added the & you basically gave the SPI the pointer to the pointer of where you want to write. So the SPI is writing the received data over the pointer, instead of at where the pointer points?
If that doesn't make sense then ask me again. It's a hard thing to explain.
Update:
This is as I understand it, not a pointer but an array?
The compiler only see's it as an pointer. In your case the pointer happen to point to an array, but it could have been to anywhere (almost) in memory. I implore you to rather think in terms of a pointer pointing to the first element of an array (*ptr==array[0]), and not in terms of an array.
Is it somehow implicit so the compiler knows what I want to do so it just accepts and compiles correctly?
I'm not sure if the compiler should compile successfully or not. But you should not rely on that. It's happens often where one could send pointers of pointers around (**ptr), so the compiler is just going to assume you know what you are doing. So you must take great care of how you work with your pointers.
Ok, after trying to solve this for a day or so, I finally found the mistake, it should not be &Data but just Data so it must look like this:
if(HAL_SPI_TransmitReceive(&hspi3, (uint8_t*)Read_Cmd, (uint8_t *)Data, (Eeprom_Page_Size +3), 5000) != HAL_OK)
{
/* Transfer error in transmission process */
Error_Handler();
}
I am not sure why that is ?
Two possible mechanisms come to mind:
IPC like the existing QMP and QAPI
QEMU loads a shared library plugin that contains the model
Required capabilities (of course all possible through the C API, but not necessarily IPC APIs):
inject interrupts
register callbacks for register access
modify main memory
Why I want this:
use QEMU as a submodule and leave its source untouched
additional advantages only present for IPC methods:
write the models in any language I want
use a non-GPL license for my device
I'm aware of in-tree devices as explained at: How to add a new device in QEMU source code? which are the traditional way of doing things.
What I've found so far:
interrupts: could only find NMI generation with the nmi monitor command
IO ports: IO possible with i and o monitor commands, so I'm fine there
main memory:
the ideal solution would be to map memory to host directly, but that seems hard:
http://kvm.vger.kernel.narkive.com/rto1dDqn/sharing-variables-memory-between-host-and-guest
https://www.linux-kvm.org/images/e/e8/0.11.Nahanni-CamMacdonell.pdf
http://www.fp7-save.eu/papers/SCALCOM2016.pdf
memory read is possible through the x and xp monitor commands
could not find how to write to memory with monitor commands. But I think the GDB API supports, so it should not be too hard to implement.
The closest working piece of code I could find was: https://github.com/texane/vpcie , which serializes PCI on both sides, and sends it through QEMU's TCP API. But this is more inefficient and intrusive, as it requires extra setup on both guest and host.
This create out of tree PCI device , it just display device in lspci..
It will ease faster PCI driver implementation as it will act as module,
can we extend this to to have similar functionality as edu-pci of QEMU.?
https://github.com/alokprasad/pci-hacking/blob/master/ksrc/virtual_pcinet/virtual_pci.c
/*
*/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sysfs.h>
#include <linux/fs.h>
#include <linux/kobject.h>
#include <linux/device.h>
#include <linux/proc_fs.h>
#include <linux/types.h>
#include <linux/pci.h>
#include <linux/version.h>
#include<linux/kernel.h>
#define PCI_VENDOR_ID_XTREME 0x15b3
#define PCI_DEVICE_ID_XTREME_VNIC 0x1450
static struct pci_bus *vbus;
static struct pci_sysdata *sysdata;
static DEFINE_PCI_DEVICE_TABLE( vpci_dev_table) = {
{PCI_DEVICE(PCI_VENDOR_ID_XTREME, PCI_DEVICE_ID_XTREME_VNIC)},
{0}
};
MODULE_DEVICE_TABLE(pci, vpci_dev_table);
int vpci_read(struct pci_bus *bus, unsigned int devfn, int where,
int size, u32 *val)
{
switch (where) {
case PCI_VENDOR_ID:
*val = PCI_VENDOR_ID_XTREME | PCI_DEVICE_ID_XTREME_VNIC << 16;
/* our id */
break;
case PCI_COMMAND:
*val = 0;
break;
case PCI_HEADER_TYPE:
*val = PCI_HEADER_TYPE_NORMAL;
break;
case PCI_STATUS:
*val = 0;
break;
case PCI_CLASS_REVISION:
*val = (4 << 24) | (0 << 16) | 1;
/* network class, ethernet controller, revision 1 */ /*2 or 4*/
break;
case PCI_INTERRUPT_PIN:
*val = 0;
break;
case PCI_SUBSYSTEM_VENDOR_ID:
*val = 0;
break;
case PCI_SUBSYSTEM_ID:
*val = 0;
break;
default:
*val = 0;
/* sensible default */
}
return 0;
}
int vpci_write(struct pci_bus *bus, unsigned int devfn, int where,
int size, u32 val)
{
switch (where) {
case PCI_BASE_ADDRESS_0:
case PCI_BASE_ADDRESS_1:
case PCI_BASE_ADDRESS_2:
case PCI_BASE_ADDRESS_3:
case PCI_BASE_ADDRESS_4:
case PCI_BASE_ADDRESS_5:
break;
}
return 0;
}
struct pci_ops vpci_ops = {
.read = vpci_read,
.write = vpci_write
};
void vpci_remove_vnic()
{
struct pci_dev *pcidev = NULL;
if (vbus == NULL)
return;
pci_remove_bus_device(pcidev);
pci_dev_put(pcidev);
}
EXPORT_SYMBOL( vpci_remove_vnic);
void vpci_vdev_remove(struct pci_dev *dev)
{
}
static struct pci_driver vpci_vdev_driver = {
.name = "Xtreme-Virtual-NIC1",
.id_table = vpci_dev_table,
.remove = vpci_vdev_remove
};
int vpci_bus_init(void)
{
struct pci_dev *pcidev = NULL;
sysdata = kzalloc(sizeof(void *), GFP_KERNEL);
vbus = pci_scan_bus_parented(NULL, 2, & vpci_ops, sysdata);
//vbus = pci_create_root_bus(NULL,i,& vpci_ops, sysdata,NULL);
//if (vbus != NULL)
//break;
memset(sysdata, 0, sizeof(void *));
if (vbus == NULL) {
kfree(sysdata);
return -EINVAL;
}
if (pci_register_driver(& vpci_vdev_driver) < 0) {
pci_remove_bus(vbus);
vbus = NULL;
return -EINVAL;
}
pcidev = pci_scan_single_device(vbus, 0);
if (pcidev == NULL)
return 0;
else
pci_dev_get(pcidev);
pci_bus_add_devices(vbus);
return 0;
}
void vpci_bus_remove(void)
{
if (vbus) {
pci_unregister_driver(&vpci_vdev_driver);
device_unregister(vbus->bridge);
pci_remove_bus(vbus);
kfree(sysdata);
vbus = NULL;
}
}
static int __init pci_init(void)
{
printk( "module loaded");
vpci_bus_init();
return 0;
}
static void __exit pci_exit(void)
{
printk(KERN_ALERT "unregister PCI Device\n");
pci_unregister_driver(&vpci_vdev_driver);
}
module_init(pci_init);
module_exit(pci_exit);
MODULE_LICENSE("GPL");
There is at least one fork of QEMU I'm aware of that offers shared library plugins for QEMU... but it's a fork of QEMU 4.0.
https://github.com/cromulencellc/qemu-shoggoth
It is possible to build out of tree plugins with this fork, though it's not documented.
On Nov 11 2019 Peter Maydell, a major QEMU contributor, commented on another Stack Overflow question that:
Device plugins are specifically off the menu, because upstream does not want to provide a nice easy mechanism for people to use to have out-of-tree non-GPL/closed-source devices.
So it seems that QEMU devs oppose this idea at that point in time. It is worth learning about the QEMU plugin system though which might come handy for related applications in any case: How to count the number of guest instructions QEMU executed from the beginning to the end of a run?
This is a shame. Imagine if the Linux kernel didn't have a kernel module interface! I suggest QEMU expose this interface, but just don't make it stable, so that it won't impose a developer burden, and which gives the upside that those who merge won't have as painful rebases.
I'm trying to use Splint with MySQL C API and have run in to some additional problems relating to freeing memory. In all the examples I can find about using the C API, the only freeing function that is called is mysql_free_result, but rows and fields are never freed:
while ((row = mysql_fetch_row(result)))
{
for(int i = 0; i < num_fields; i++)
{
if (i == 0)
{
while(field = mysql_fetch_field(result))
{
// Bla
}
}
}
}
mysql_free_result(result);
mysql_close(con);
Splint will of course throw an error saying that row and field are memory leaks. Are they? How to resolve this? Should I manually free the row and field structs?
Edit: OK, since mysql_fetch_row returns null when there is no more rows, I assume it also frees all memory from former row each loop. But how the hell would I tell Splint this?
EDit 2: Here's the implementation for mysql_fetch_row (version 5.5). No memory is allocated, the function just point you to the next row. So what's needed is a Splint annotation for the function that tells Splint no memory is allocated, but shared.
MYSQL_ROW STDCALL
mysql_fetch_row(MYSQL_RES *res)
{
DBUG_ENTER("mysql_fetch_row");
if (!res->data)
{ /* Unbufferred fetch */
if (!res->eof)
{
MYSQL *mysql= res->handle;
if (mysql->status != MYSQL_STATUS_USE_RESULT)
{
set_mysql_error(mysql,
res->unbuffered_fetch_cancelled ?
CR_FETCH_CANCELED : CR_COMMANDS_OUT_OF_SYNC,
unknown_sqlstate);
}
else if (!(read_one_row(mysql, res->field_count, res->row, res->lengths)))
{
res->row_count++;
DBUG_RETURN(res->current_row=res->row);
}
DBUG_PRINT("info",("end of data"));
res->eof=1;
mysql->status=MYSQL_STATUS_READY;
/*
Reset only if owner points to us: there is a chance that somebody
started new query after mysql_stmt_close():
*/
if (mysql->unbuffered_fetch_owner == &res->unbuffered_fetch_cancelled)
mysql->unbuffered_fetch_owner= 0;
/* Don't clear handle in mysql_free_result */
res->handle=0;
}
DBUG_RETURN((MYSQL_ROW) NULL);
}
{
MYSQL_ROW tmp;
if (!res->data_cursor)
{
DBUG_PRINT("info",("end of data"));
DBUG_RETURN(res->current_row=(MYSQL_ROW) NULL);
}
tmp = res->data_cursor->data;
res->data_cursor = res->data_cursor->next;
DBUG_RETURN(res->current_row=tmp);
}
}
The correct annotation for sharing read-only storage is /*#observer#*/. For sharing writeable storage, /*#exposed#*/ could be used.
/*#observer#*/ MYSQL_ROW STDCALL mysql_fetch_row(MYSQL_RES *result);
More in the Splint manual.
I've created a MySQL User defined function to open a unix domain type socket.
My problem is that if I call my function directly like so:
SELECT socketOpen("/path/to/file", "message");
It always executes in <10ms. So that is nice. But since I don't want to manually call this function everytime, I've created a stored procedure which does an insert into database and then calls this function.
The problem I'm facing is that the stored procedure usually takes <10ms, but somestimes takes over 1s. Even 5s. I don't understand how this happens. Is there a caching problem or something ?
Below is the code is use, stripped of error checking for clarity:
char *socketOpen(UDF_INIT *initid __attribute__((unused)),
UDF_ARGS *args, char *result, unsigned long *length,
char *is_null, char *error __attribute__((unused)))
{
int sockfd, portno, n, servlen;
struct sockaddr_un serv_addr;
struct hostent *server;
char socket_path[100];
char message[100];
memcpy(socket_path,args->args[0],args->lengths[0]);
socket_path[args->lengths[0]] = 0;
memcpy(message,args->args[1],args->lengths[1]);
message[args->lengths[1]] = 0;
sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sun_family = AF_UNIX;
strcpy(serv_addr.sun_path, args->args[0]);
servlen=strlen(serv_addr.sun_path) + sizeof(serv_addr.sun_family);
connect(sockfd,(struct sockaddr *) &serv_addr, servlen);
n = write(sockfd, message, strlen(message));
bzero(message,100);
n = read(sockfd, message, 100);
close(sockfd);
strcpy(result, message);
*length = strlen(message);
return result;
}
I would appreciate your insight into this problem. Thank you.
Since I've got no replies and I've fixed the problem I would like to share my solution to the problem.
The cause of the problem was quite different than I ancipated.
The machine of running the above code was Raspberry pi, which slowness I did not take into account. As it turns out most of the delay was caused by the UPDATE statement in the procedure. As soon as I changed the table ENGINE to MyISAM everything went smooth from then on.
Altough while testing the code there was sometimes still a slight delay. I've fixed that with making the socket non-blocking. That means that if something will go wrong the socket will never be opened, but I figure that is better than blocking indefinetely.
I do realise that this problem is pretty common, but I have spent around 4 days so far, trying to fix it on my own, using all the smart advice I found on the Internet and - unfortunately - I've failed.
I managed to make openCV2.4.6 work with my VisualStudio 2012, or at least that's what I assumed after I was able to stream a video from my webcam with this example:
#include "stdafx.h"
#include "opencv2/opencv.hpp"
int main( int argc, const char** argv )
{
CvCapture* capture;
IplImage* newImg;
while (true)
{
capture = cvCaptureFromCAM(-1);
newImg = cvQueryFrame( capture );
cvNamedWindow("Window1", CV_WINDOW_AUTOSIZE);
cvShowImage("Window1", newImg);
int c = cvWaitKey(10);
if( (char)c == 27 ) { exit(0); }
}
cvReleaseImage(&newImg);
return 0;
}
Everything worked fine, so I decided to play around with it and I made an attempt to use a simple image processing operation such as converting rgb to grayscale. I modified my code to following:
#include "stdafx.h"
#include "opencv2/opencv.hpp"
int main( int argc, const char** argv )
{
CvCapture* capture;
IplImage* img1;
IplImage* img2;
while (true)
{
capture = cvCaptureFromCAM(-1);
img1 = cvQueryFrame( capture );
img2 = cvCreateImage(cvGetSize(img1),IPL_DEPTH_8U,1);
cvCvtColor(img1,img2,CV_RGB2GRAY);
cvNamedWindow("Window1", CV_WINDOW_AUTOSIZE);
cvNamedWindow("Window2", CV_WINDOW_AUTOSIZE);
cvShowImage("Window1", img1);
cvNamedWindow("Window2", CV_WINDOW_AUTOSIZE);
int c = cvWaitKey(10);
if( (char)c == 27 ) { exit(0); }
}
cvReleaseImage(&img1);
cvReleaseImage(&img2);
return 0;
}
And that's the place where the nightmare started. I keep getting the
Unhandled exception at at 0x000007FEFD57AA7D in opencvbegginer.exe: Microsoft C++ exception: cv::Exception at memory location 0x000000000030F920.
I did some research and tried few solutions, such as exchanging opencv_core246.lib to opencv_core246d.lib, etc. For a second I hoped it might work, but the reality punched me again with msvcp100d.dll missing. I tried to update all redistributable packages, but it didn't change the fact I keep getting this error. I tried to find out how to fix it another way and I found some forum on which they tell to go to C/C++ properties and change the Runtime Library to MTd, so... I tried this as well, but - as you can notice by now - it didn't work.
At this current moment I just ran out of ideas on how to fix this, so I would be really grateful for any help.
Cheers
PS. Important thing to add: when I got the unhandled exception, opencv 'spoke to me', saying
OpenCV Error: Bad argument in
unknown function, file ......\scr\opencv\modules\core\src\array.cpp,
line 1238
However, I already assumed way back then that I'm just not clever enough with my idiot-resistant code and I tried few other pieces of code that were written by competent people - unfortunately, I keep getting exactly the same error (the rest is the same as well, after I change the things mentioned above).
If img1 == NULL, then it crashes on cvGetSize(img1). Try enclosing the code after cvQueryFrame in an if (img1 != NULL).
However, if it returns NULL for every frame, it means there is something wrong with your camera/drivers/way you capture the frames.
You should also move the cvNamedWindow outside of the loop, since there is no need for it to be recreated for every frame.