Changes between Version 39 and Version 40 of io_operations


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Timestamp:
Jan 16, 2018, 6:33:52 PM (4 years ago)
Author:
alain
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  • io_operations

    v39 v40  
    144144The target hardware architectures generally provide a variable - but bounded - number of text terminals (called TXT channels in ALMOS-MKH). This NB_TXT_CHANNELS number is an hardware parameter defined in the ''arch_info.bin'' file. We describe here how ALMOS-MKH uses these terminals:
    145145 1. The TXT[0] terminal is reserved for the kernel. It is normally used by the kernel to display log and/or debug messages. It can only be used by the user processes for debug, through some specific system calls such as the panic() or display_xxx() functions, that should not be used in normal exploitation.
    146  1. The other (NB_TXT_CHANNELS - 1) terminals TXT[i] are shared resources used by all user processes. During kernel initialization,  ALMOS-MKH creates the first ''INIT'' user process, that creates itself (NB_TXT_CHANNELS -1) ''KSH'' user processes (one shell per user text terminal). All user process created by the KSH[i] process
    147 share the same TXT[i] terminal, and belong to the same ''group'' of process. 
    148  1. In normal use, the ''KSH[i]'' processes should not be destroyed. If a ''KSH[i]'' process is killed, it is automatically recreated by the ''INIT'' process, to guaranty that there is always one ''KSH[i]'' for each TXT_i terminal.
    149  1. Regarding the WRITE accesses, all processes attached to the same TXT_TX[i] terminal can atomically display character strings without any guaranty on the order, when these strings are displayed by different process. The strings providing from various processes are simply sequentialized by the kernel thread associated to the shared TXT_TX[i] device.
    150  1. Regarding the READ accesses, only one process the group of process attached to the TXT[i] terminal (called  ''foreground'' process) is the owner of the TXT_RX[i] terminal, and can read characters. The other processes (called ''background'' processes) should not try to read characters. If a background process P try to read, it receives a SIGSTOP signal, and will keep blocked until the user uses the ''fg'' shell command to give P the ownership of the TXT_RX[i] terminal.
     146 1. The other (NB_TXT_CHANNELS - 1) terminals TXT[i] are shared resources used by all user processes. During kernel initialization,  ALMOS-MKH creates the first INIT user process, that creates itself (NB_TXT_CHANNELS -1) KSH user processes (one shell per user text terminal). All user process created by the KSH[i] process share the same TXT[i] terminal, and belong to the same group of process. 
     147 1. In normal use, the KSH[i] processes is not supposed to be killed. If a KSH[i] process is killed, it is automatically recreated by the INIT process, to guaranty that there is always one KSH[i] for each TXT[i] terminal.
     148 1. Regarding the WRITE accesses, all processes attached to the same TXT_TX[i] terminal can atomically display character strings. There is no guaranty on the order, when these strings are displayed by different process., because these strings are simply sequentialized by the kernel thread associated to the shared TXT_TX[i] device.
     149 1. Regarding the READ accesses, only one process in the group of process attached to the TXT[i] terminal (called  ''foreground'' process) is the owner of the TXT_RX[i] terminal, and can read characters. The other processes (called ''background'' processes) should not try to read characters. If a background process P try to read, it receives a SIGSTOP signal, and will keep blocked until the user uses the ''fg'' shell command to give P the ownership of the TXT_RX[i] terminal.
    151150 
    152151== I) Hardware Specific  ==