Messages in this thread | | | Date | Tue, 17 Jun 2008 23:26:56 +0800 | From | "Bob Zhang" <> | Subject | Re: Does anyone run AXFS in 2.4 version of kernel ? I am trying my best to apply AXFS patches into 2.4.18 |
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Following is what I have known about AXFS implement .If I am not right, please Jared Hulbert cto correct what I have said.
Honestly speaking , AXFS orgnization is pure complex , and no any valuable document to help to understand the source code . if you want to make clear what happned ,it is not easy .
I have spent over 2 days to read the mkfs.axfs.c , this is what I have known . --- For axfs super block ,the best valuable infomation is some offset of regions , axfs image has many regions , such as node_type regions , node_index regions,especially X IP region,Compressed region and Byte Aligned region which are the most important for us.
Important info is that once you have read the superblock into a buffer head , you can get all the offset info of all regions. thus , you can get the address of regions in the file image . once you get the region structure , you can get the "region->fsoffset" and "region->virt_addr" , the "region->fsoffset" present that the real location region in the image . For example , for XIP region , you can get all the pages of data through "xip_region->fsoffset" . and then through node_index, you can get responding pages.
Another key parameter is "virt_addr" ,
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First ,pages are of XIP or Compressed is decided by mkfs.axfs -i xml.txt if no the xml.txt provided , mkfs.axfs should compress all the files in the image by default.
in the main() of mkfs.axfs.c the axfs will compute the number of files , there are some global variables to record these . in function named parese_directory() it will generate many entries reponding with these files ,and at last , it will call "is_xipfile()" function to call "set_page_state" function to set some files and pages to be XIP if these names occur in the xml file as parameter of mkfs.axfs -i .
In fact , for XIP files and pages , axfs handling is simple , for example , I want to set rootfs/init 's 0~4095 bytes to be XIP ,the length of block of data must be aligned with PAGE_SIZE . you can set the <chunk> <size>4096</size> <offset>0</offset> </chunk>
In fact , the data of XIP and that of compressed will be stored respectively different regions . for example , a file size is large , you know ,for example ,3MB . it will have many pages of data , only the XIP pages will be stored into XIP region node_index[node_count] = xip_rd.size/PAGE_SIZE . THIS INDEX is valid for XIP
For every page , it will have node_index. this node_index will be added when parsing the root directory . that is also said that, every page has its own unique index number . Future , in kernel ,the axfs code will use it. the kernel axfs code will use some macros to get detailed infomation about a page , for example , this page is of XIP or Compressed .
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