Hello Heinrich, Patch applied, with a few minor wording/spelling tweaks. One change (addition) below. On 01/27/2015 10:27 PM, Heinrich Schuchardt wrote: > With his last patches for getrandom.2 Michael Kerrisk posed a few > questions and left some comments in the man-page. This patch > seeks to clarify the open issues. > > 72 For example, if the call is interrupted by a signal handler, > 73 it may return a partially filled buffer, or fail with the error > 74 .BR EINTR . > 75 .\" Tested with buffer sizes > 256 bytes: both partial reads > 76 .\" and EINTR can occur, with the former being more frequent. > 77 .\" > > Michael's observation agrees with the code. > For buffer size > 256: If the buffer is still empty EINTR occurs. If > any number of bytes has been read to the buffer, that number is returned. > The comment can be removed. > > 78 .\" mtk: In the absence of signals, in my testing, even very large reads > 79 .\" return full buffers. I found that reads of up to 33554431 always > 80 .\" returned a filled buffer. Specifying 'buflen' > 33554431 always > 81 .\" returned just 33554431 bytes. (I'm not sure where that number comes > from. > > The maximum number of bytes transferred is limited for /dev/urandom to > nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3)); > // <= 0x1fffff > > and for /dev/random to > nbytes = min_t(size_t, nbytes, SEC_XFER_SIZE); // <= 0x200 Ahh -- thanks for uncovering that. > Lets put this into the NOTES section. > > 224 When reading from > 225 .IR /dev/random , > 226 blocking requests of any size can be interrupted by a signal > 227 (the call fails with the error > 228 .BR EINTR ). > > Thats ok. > > 82 If the pool has not yet been initialized, then the call blocks, unless > 83 .B GRND_RANDOM > 84 is specified in > 85 .IR flags . > 86 .\" FIXME We need a bit more information here. > 87 .\" The reader will ask: when is /dev/urandom initialized? > 88 .\" There should be some text here to explain that. > > Entropy is collected from different sources, e.g. > - time of reaping a thread > - MAC address of a network interfaces > - Allwinner security ID > - ROM content of a firewire device > - ... > > When more than 128 bits have been collected, the pool is set to initialized. > > I suggest that detailed information about the initialization should be provided > on the random.4 page. Yes, that would be more appropriate. > > I added a paragraph in the NOTES section. Thanks! > Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx> > --- > man2/getrandom.2 | 29 +++++++++++++++++++---------- > 1 file changed, 19 insertions(+), 10 deletions(-) > > diff --git a/man2/getrandom.2 b/man2/getrandom.2 > index f66cebe..469da27 100644 > --- a/man2/getrandom.2 > +++ b/man2/getrandom.2 > @@ -72,20 +72,10 @@ No such guarantees apply for larger buffer sizes. > For example, if the call is interrupted by a signal handler, > it may return a partially filled buffer, or fail with the error > .BR EINTR . > -.\" Tested with buffer sizes > 256 bytes: both partial reads > -.\" and EINTR can occur, with the former being more frequent. > -.\" > -.\" mtk: In the absence of signals, in my testing, even very large reads > -.\" return full buffers. I found that reads of up to 33554431 always > -.\" returned a filled buffer. Specifying 'buflen' > 33554431 always > -.\" returned just 33554431 bytes. (I'm not sure where that number comes from. > If the pool has not yet been initialized, then the call blocks, unless > .B GRND_RANDOM > is specified in > .IR flags . > -.\" FIXME We need a bit more information here. > -.\" The reader will ask: when is /dev/urandom initialized? > -.\" There should be some text here to explain that. > > The > .I flags > @@ -179,6 +169,25 @@ was introduced in version 3.17 of the Linux kernel. > .SH CONFORMING TO > This system call is Linux-specific. > .SH NOTES > +.SS Maximum number of bytes returned > +As of Linux 3.19 the following limits apply: > +.IP * 3 > +When reading from > +.I /dev/urandom > +a maximum of 33554431 bytes is returned by a single call to > +.BR getrandom () > +on a system where > +.I int > +has a size of 32 bits. > +.IP * > +When reading from > +.I /dev/random > +a maximum of 512 bytes is returned. > +.SS Initilization of the entropy pool > +The kernel collects bits of entropy from environment. > +When a sufficient number of random bits has been collected the > +.I /dev/urandom > +entropy pool is set to initialized. I added a sentence here: This state is normally reached early in the system bootstrap phase. > .SS Interruption by a signal handler > A call to > .BR getrandom () Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
