Re: [dev] sanei_scsi.c and Linux versions < 2.2.7

From: abel deuring (a.deuring@satzbau-gmbh.de)
Date: Mon Jul 16 2001 - 04:27:40 PDT

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    Douglas Gilbert wrote:
    > > Well, the error report could of course be added to sanei_scsi_req_enter,
    > > but a backend should check for this error in sanei_scsi_req_wait too: If
    > > you queue two or more commands and the low level driver does not support
    > > command queueing, sanei_scsi_req_enter puts the second and following
    > > commands into its internal queue, so it cannot return an error from the
    > > SG driver.
    >
    > The reserved buffer is only good for one SCSI command
    > at a time (per file descriptor) and only if it is big
    > enough to hold the size of transfer being requested.
    >
    > Thus when commands are queued there is a risk that
    > subsequent commands will fail with ENOMEM. This "out of
    > memory" situation is more likely to occur with ISA
    > SCSI adapters which can only use the bottom 16 MB of
    > memory for DMA. This is not a hard error and should
    > not be treated as such [IMO]. The reserve buffer
    > more or less guarantees SANE can queue 1 command.
    > If memory is not available to queue 2 or more commands
    > then wait ....

    Doug,

    thanks for helping my memory :) I knew there were even more reasons to
    check ENOMEM late, but I could not remember them while I wrote my mail.

    Abel

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