>Number: 148581
>Category: misc
>Synopsis: fopen fails with EMFILE if there are more than SHORT_MAX fds
>open
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Tue Jul 13 21:30:07 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator: Manish Vachharajani
>Release: 7.3-RELEASE
>Organization:
LineRate Systems
>Environment:
FreeBSD wks1.int.lineratesystems.com 7.3-RELEASE FreeBSD 7.3-RELEASE #0: Fri
Jul 2 12:56:26 MDT 2010
[email protected]:/usr/obj/usr/src/sys/DEV73PMC amd64
>Description:
fopen will fail with EMFILE if there are more than SHORT_MAX file descriptors
open in the process. It does not matter that these fds were not created by
fopen.
To make matters worse gcc's libstdc++ uses fopen and friends to implement
ofstream so those function mysteriously fail if there are more than 32k fds
open in the process.
>How-To-Repeat:
To reproduce the problem compile and run:
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#define BIGNUM 50000
int main(int argc, char *argv[]) {
int i;
int fds[BIGNUM];
for(i=0; i < BIGNUM; ++i) {
fds[i] = open("/dev/null", O_RDONLY);
}
FILE *fil = fopen("/dev/null", "r");
if(fil == NULL) {
fprintf(stderr, "Could not open /dev/null: %s\n" , strerror(errno));
}
for(i=0; i < BIGNUM; ++i) {
close(fds[i]);
}
return 0;
}
>Fix:
The simple fix is to make _file from struct sFILE { ... } FILE; in stdio.h an
int instead of a short. However, this will break binary compatibility with
anyone compiled with an old libc.
A very dirty fix that would not break binary compatibility is, for each
architecture, use the open space from the padding and alignment requirements of
FILE to stash the other bits of _file and make all users of FILE use an
accessor macro that pulls out the right bits.
A quick fix to double the threshold at which the problem occurs would be to
make _file an unsigned short and use the all 1's value to indicate that this is
not a file resource. Not sure if this will work either, though.
>Release-Note:
>Audit-Trail:
>Unformatted:
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