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libfsdriver: clear VM cache only if used

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As part of its built-in mmap emulation support for "none" file system
services, libfsdriver clears the VM cache upon exit.  However, for
trivial file systems which do not even support reading from files, the
the VM cache need to be cleared either.  With this patch, the VM cache
is cleared only when modified, so that such trivial file systems need
not be given CLEARCACHE permission.

Change-Id: I518c092443455302b9b9728f10a3f894d2c8036b
This commit is contained in:
David van Moolenbroek 2015-06-22 11:50:04 +00:00
parent 3f30eb69f0
commit 0a2a08739e
1 changed files with 6 additions and 1 deletions
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7
minix/lib/libfsdriver/call.c
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@ -3,6 +3,8 @@
#include <minix/ds.h>
#include <sys/mman.h>
static int fsdriver_vmcache; /* have we used the VM cache? */
/*
* Process a READSUPER request from VFS.
*/
@ -59,6 +61,7 @@ fsdriver_readsuper(const struct fsdriver * __restrict fdp,
fsdriver_mounted = TRUE;
fsdriver_device = dev;
fsdriver_root = root_node.fn_ino_nr;
fsdriver_vmcache = FALSE;
}
return r;
@ -77,7 +80,7 @@ fsdriver_unmount(const struct fsdriver * __restrict fdp,
fdp->fdr_unmount();
/* If we used mmap emulation, clear any cached blocks from VM. */
if (fdp->fdr_peek == NULL && major(fsdriver_device) == NONE_MAJOR)
if (fsdriver_vmcache)
vm_clear_cache(fsdriver_device);
/* Update library-local state. */
@ -256,6 +259,8 @@ builtin_peek(const struct fsdriver * __restrict fdp, ino_t ino_nr,
pos, &flags, nbytes, VMSF_ONCE);
if (r == OK) {
fsdriver_vmcache = TRUE;
dev_off += nbytes;
r = nbytes;