MMAP尝试将缓冲区缓冲区加倍时失败 [英] MMAP fails in attempt to double buffer framebufer
问题描述
我正在尝试使用ioctl(fd，FBIOPAN_DISPLAY ... 我的单个缓冲区代码可以正常工作
I am trying to implement a double buffer using ioctl(fd, FBIOPAN_DISPLAY... my single buffer code works fine
screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
fbp = (char*)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);
当我尝试通过使用screensize * 2来增加长度参数"时，mmap失败，并显示EINVAL.我认为它不喜欢我的length参数.
when I try to increase the "length parameter" by using screensize*2, the mmap fails with EINVAL. I think it doesn't like my length parameter.
单个缓冲区的屏幕大小为6,220,800，而双缓冲区的屏幕大小为12,441600.这是一个嵌入式系统，但具有1 Gig的RAM.
The screen size for a single buffer is 6,220,800 and for the double buffer is 12,441600. This is an embedded system but it has 1 Gig of RAM.
length参数是size_t，在这个系统上只有4个字节，这使我认为我可以使用的最大大小为4 Meg，但是6 Meg可以正常工作，所以我认为我缺少了一些非常简单的东西.有没有办法mmap大于size_t的缓冲区?
The length parameter is size_t which on this system is only 4 bytes which would make me think that the max size I could use would be 4 Meg, yet 6 Meg works fine so I think I am missing something really simple. Is there a way to mmap a buffer larger than size_t?
推荐答案
手册页表示长度(第二个参数)的类型为size_t，所以我认为传递较大的类型是不安全的.
The man page says that length (the 2nd parameter) is of type size_t, so I don't think you are safe to pass a larger type.
I would suggest you to just map the first part, and then remap the second part as shown in this SO Q&A.
关于EINVAL:
手册页中说明了以下内容:
Regarding the EINVAL:
Following is stated in the man page:
EINVAL 我们不喜欢addr，length或offset(例如，它们太大或在页面边界上未对齐).
EINVAL We don't like addr, length, or offset (e.g., they are too large, or not aligned on a page boundary).
EINVAL (从Linux 2.6.12开始)长度为0.
EINVAL (since Linux 2.6.12) length was 0.
EINVAL 标志既不包含MAP_PRIVATE也不包含MAP_SHARED，也不包含这两个值.
EINVAL flags contained neither MAP_PRIVATE or MAP_SHARED, or contained both of these values.
您确定您对页面感兴趣吗?
Are you sure you are page alligned?
这篇关于MMAP尝试将缓冲区缓冲区加倍时失败的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
