Messages in this thread Patch in this message | | | Subject | [patch] file position update when reading /dev/kmem | Date | Mon, 10 May 1999 23:02:51 +0100 | From | Steven Hand <> |
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When read()'ing from /dev/kmem, the file position is incorrectly updated, which bites you if you perform >1 read on the file before close()'ing it. AFAICS, the bug has been around since at least 2.1.127.
The tiny patch attached below is against 2.2.7 and should fix the problem. Notice that the first part of the patch is simply an optimisation to avoid calling vread() and iterating along every vmalloc'd area in the case that copy_to_user() has already done its stuff. The line involving the update of *ppos is the important one.
S.
--- v2.2.7/linux/drivers/char/mem.c Mon May 10 22:29:38 1999 +++ linux/drivers/char/mem.c Mon May 10 22:27:59 1999 @@ -247,11 +247,14 @@ count -= read; } - virtr = vread(buf, (char *)p, count); - if (virtr < 0) - return virtr; - *ppos += p + virtr; - return virtr + read; + if(count) { + if((virtr = vread(buf, (char *)p, count)) < 0) + return virtr; + read += virtr; + } + + *ppos += read; + return read; } /*
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