 |
 |
 |
 |
 |
|
|
|
|
|
|
|
This procedure is called by “open” (5774) and “creat” (5793, 5795), passing values of the third parameter, “trf”, of 0, 2 and 1 respectively. The value 2 represents the case where no file of the desired name already exists.
The second parameter, “mode”, can take the values 01 (“FREAD”), 02 (“FWRITE”) or 03 (“FREAD | FWRITE”) when “trf” is 0, but only 02 otherwise;
Whete a file of the desired name already exists, check the access permissions for the desired mode(s) of activity via calls on “access” (6746), which may set “u.u_error” as a side-effect;
If the file is being “created”, eliminate its previous contents via a call on “itrunc” (7414). The code here could be improved by changing the test to “(trf == 1)”. Verify that this would be so.
“prele” (7882) is used to “unlock” “inodes”. Where, you may ask, did the “inode” get “locked”, and why?
Note that “falloc” (6847) calls “ufalloc” (6824) as the first thing it does;
“ufalloc” leaves the user file identifying number “u.u_ar0[R0]”. Why does this statement occur where it does, instead of after line 5834?
“openi” (6702) is called to call handlers for special files, in cae any device specific actions are required (for disk files there is no action);
In the case of an error while making the “file” array entry, the “inode” entry is released by a call on “iput”.
It will be seen that responsibility is quite widely distributed. The “file” table entry is initialised by “falloc” and “openl”; the “inode” table entry, by “iget”, “ialloc” and “maknode”.
Note that “ialloc” clears out the “i_addr” array of a newly allocated “inode” and “itrunc” does the same for a pre-existing “inode”, so that after the “creat” system call, there are no disk blocks associated with the file, now classed as “small”.
|
|
|
|
|
|