Re: [PATCH v3 3/3] man2/fincore.2: document general description about fincore(2)
flat view
From: Dave Hansen <hidden>
Date: 2014-07-07 19:08:38
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linux-mm, lkml
On 07/07/2014 11:00 AM, Naoya Horiguchi wrote:
quoted hunk ↗ jump to hunk
+.SH RETURN VALUE +On success, +.BR fincore () +returns 0. +On error, \-1 is returned, and +.I errno +is set appropriately.
Is this accurate? From reading the syscall itself, it looked like it did this:
quoted hunk ↗ jump to hunk
+ * Return value is the number of pages whose data is stored in fc->buffer. + */ +static long do_fincore(struct fincore_control *fc, int nr_pages)
and:
+SYSCALL_DEFINE6(fincore, int, fd, loff_t, start, long, nr_pages,
...
quoted hunk ↗ jump to hunk
+ while (fc.nr_pages > 0) { + memset(fc.buffer, 0, fc.buffer_size); + ret = do_fincore(&fc, min(step, fc.nr_pages)); + /* Reached the end of the file */ + if (ret == 0) + break; + if (ret < 0) + break;
...
+ }
...
+ return ret; +}
Which seems that for a given loop of do_fincore(), you might end up returning the result of that *single* iteration of do_fincore() instead of the aggregate of the entire syscall. So, it can return <0 on failure, 0 on success, or also an essentially random >0 number on success too. Why not just use the return value for something useful instead of hacking in the extras->nr_entries stuff? Oh, and what if that
+ if (extra) + __put_user(nr, &extra->nr_entries);
fails? It seems like we might silently forget to tell userspace how many entries we filled.