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vfs: use the sentinel trick in locked lookup path parsing

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(cherry picked from commit d81aefa8b7)
This commit is contained in:
Mateusz Guzik 2021-05-25 19:34:26 +02:00
parent a1ef0386c9
commit a138a50c75
1 changed files with 16 additions and 1 deletions
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17
sys/kern/vfs_lookup.c
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@ -850,6 +850,7 @@ lookup(struct nameidata *ndp)
{
char *cp; /* pointer into pathname argument */
char *prev_ni_next; /* saved ndp->ni_next */
char *nulchar; /* location of '\0' in cn_pnbuf */
struct vnode *dp = NULL; /* the directory we are searching */
struct vnode *tdp; /* saved dp */
struct mount *mp; /* mount table entry */
@ -909,9 +910,23 @@ dirloop:
* cnp->cn_nameptr for callers that need the name. Callers needing
* the name set the SAVENAME flag. When done, they assume
* responsibility for freeing the pathname buffer.
*
* Store / as a temporary sentinel so that we only have one character
* to test for. Pathnames tend to be short so this should not be
* resulting in cache misses.
*/
for (cp = cnp->cn_nameptr; *cp != 0 && *cp != '/'; cp++)
nulchar = &cnp->cn_nameptr[ndp->ni_pathlen - 1];
KASSERT(*nulchar == '\0',
("%s: expected nul at %p; string [%s]\n", __func__, nulchar,
cnp->cn_pnbuf));
*nulchar = '/';
for (cp = cnp->cn_nameptr; *cp != '/'; cp++) {
KASSERT(*cp != '\0',
("%s: encountered unexpected nul; string [%s]\n", __func__,
cnp->cn_nameptr));
continue;
}
*nulchar = '\0';
cnp->cn_namelen = cp - cnp->cn_nameptr;
if (cnp->cn_namelen > NAME_MAX) {
error = ENAMETOOLONG;